Best way to understand this if you don't have the pleasure of trying for yourself is to know what actually changed - note: there may be some informed opinion involved.
Full disclosure - I like my road cars to have the 'lotus school' of suspension set up. This is to say plenty of wheel travel and more initial body roll compared to the stiffly sprung 'sporty-feeling-for-the-sake-of-excitement' approach to generic sports car set-up.
Think about the way a Lotus Evora drives down a typical UK country road - (if you haven't tried one it is worth a test drive just for enlightenment) vs. The way something like an MSport BMW or at the extreme a Nissan GTR pummels its way down the road with high spring rates and stiff anti-roll bars.
So What Changed?
Ferrari measures and benchmarks progress of its road cars in terms of outright lap times around Fiorano along with and ever increasing escalation of specific engine power as its main messaging in marketing its product range evolution. The HGTE was -0.6 second quicker around Fiorano all of which can be accounted for by the softer rubber and quicker TCU software.
This, along with how Ferrari launches product - i.e. journalists either driving or being taken on 3 passenger laps at Fiorano
before road driving have therefore become a big focus of the story and the brand.
When the standard 599 came out it was possible, at launch for
a small number of the more capable journalists in the three laps allowed to provoke understeer at Fiorano on cars with the base level standard 19" front and 20" rears and steel brakes. Tiff Needell in particular criticised the car publicly for that. EVO magazine by contrast called it the best handling GT in the world at the time and it was indeed EVO's car of the year, a rare event for the brand. Harry Metcalfe had lived with its predecessor as a long termer and so was probably the better placed journo at the time to evaluate the car but that's partially subjective on my part. The issue with a few laps at Fiorano for Tiff is that racing drivers rightly think all road cars are by comparison to an actual track / race car terrible on track as in most cases after half a lap the tyres are usually overheated, brakes are fading and warning lights are flashing all over the dash. With only three laps to do it in what are you going to do?
So the standard optioned car had too much tendency to understeer?
On standard wheels - yes, it seems so (from one report).
I can't verify that but can imagine its possible.
It is easy to adjust out this tendency out with the rest of the stock component set-up if the components are in good condition however the stock wheels are said by Ferrari themselves to be not as good selection as a base and hence why they are not valued at all in the used market. On the optional challenge wheels however and with the right geo and suspension set-up almost all of the understeer can be eliminated by set-up alone. The £14k optional HGTE pack was in the words of EVO magazine "essentially a suite of suspension, tyre and rim changes – which are, at best, a finessing of the 599’s already exemplary road manners, essentially bumping the car up a couple of notches on the hardcore scale."
Industry cynics would call it what used to be a
decals and rims flagging sales figures upgrade. [Think Vauxhall's tired model refreshes of the 80's]
The actual changes made were minimal - monogrammed but existing sports carbon seat option, CCM brakes as standard, different compound Pirelli's, 16% and 10% Stiffer springs (front and rear), 10% stiffer (and thicker) rear anti-roll bar, -10mm ride height necessitating upgraded bump stops. Leaving the factory half a degree more negative camber at the front and faster gear change software loaded into the TCU. Cosmetically the sports seats got some stitching and there was a specific to type wheel sized just like the original challenge wheel option but in a split rim design.
Of all of things that matter to a 599 the wheels are the key.
Mine already had the seats and challenge rims 20" (front and rear)
So I did a
geometry adjustment on my car (see my 599 thread) - £ Labour cost
Springs - kept them stock as I didn't want extra stiffness
Ride height actually +5mm over stock as I do road events with it and from the factory it was too low for me.
Anti-roll bars kept them stock but with custom made adjustable drop links and upgraded bushes - £One hour labour and materials
Tyres upgraded to the later homologated (and far superior Michelins)
Gearbox and ECU software upgraded by my local dealer during routine service (note only possible after a certain chassis number - later cars)
If handling better means 'goes down a typical road quicker and with more composure' then my car now does that far better than an HGTE and GTO variant and I will take that Pepsi challenge all day long. If better means does better lap times on track again I would take that challenge too - tbh the michelins are most of that difference anyway. If however handling better means 'feels more dramatic and exciting' or 'more planted' then the HGTE and GTO variants would win with drivers that value that.
Personally I think the HGTE variant is not worth any kind of premium unless you really want the wheel design and / or the added kudos of 'limited' status or any 'added value' that may confer.
If you think you may reach the limits on the standard car on 20's then have the geo done and try again. If you need to go beyond that get some GTO wheels, if you unstick those especially the front end on the road then hats off. It took two further runnings of the Mille Miglia to find the upper limit on the road of the front end for me and it happened once in a 1,000 miles on the Futa Pass. I subsequently have switched to a GTO wheel set and its trick rubber but it is now right on the point of the benefits barely outweighing the down-sides on the road with only a meaningful gain on track.
The 599 is a ridiculously capable car on 20inch wheels and fresh rubber.
If it has sports carbon seats then tweak the geo change a couple of rear ARB bushes an you pretty much have the HGTE.
Lowering and stiffening is easy with the stock coilovers.
£15k was a stiff premium in period and nothing like the targeted 40% of sales optioned it so...
Try them both and see what you really need.
OG press release here
http://joemacari.com/downloads/pdf/599 HGTE Package text.pdf
Period review
https://youtu.be/MVQs33b1Q50
Tiff's response (note: Stirling Moss's priceless reaction @ 5:20)
https://youtu.be/Ic_Cox7F0-g
