I haven’t done any online GT3 racing yet, but just looking at the car list, I am kinda confused:
¯\_(ツ)_/¯
Does anybody even understand the unfathomable mess of GT regulations?
The Car Pass and Race Day Car Pack added a bunch of Forza GT racecars, so you’re bound to meet car you don’t have access to if you don’t have these. The list they posted for GT2 and GT3 has 9 and 13 cars respectively, with 1 and 8 DLC cars respectively.
T10 made a mess by using GT2 moniker for GTE cars (which are closely related to GT3), while real GT2 cars featured in the game are KTM X-Bow GT2 and Porsche 935 (or at least Kunos Simulazioni put the latter in GT2 Pack for Assetto Corsa Competizione). At least the upcoming separate Forza GT4 division should avoid causing such confusion (apart from the fact that it contains only two cars… unless more are planned to be added with Update 11) 
Anyway, I expected more thoughtful and significant changes when T10 announced splitting Forza GT into several divisions. And I expected this to affect the entire game, not only Featured Multiplayer…
Right. There’s the “old” GT2 class maintained by the ACO and IMSA which ran from 2005-2010 and was intended to slot in below GT1 in terms of speed and performance. GT1 was dropped in 2011, and GT2 then became known as GTE (or just GT in the US).
Then there’s the “new” GT2 class, which is a completely different set of regulations. Confusingly, the cars are intended to slot in between GT4 and GT3 in terms of performance - more power than GT3, but not capable of generating anywhere near the same level of downforce. So, faster on the straights but less speed in the corners and slower laptimes overall.
I haven’t played FM23 in a while (not since shortly after update 9), but it sounds like Turn 10 has gone and taken cars from both regulation sets and put them together under the GT2 name? Which I guess would technically be accurate, but obviously is going to lend itself to confusion as well as some pretty unbalanced racing unless there is some major (and probably unrealistic) BoP applied.
So what would people say is the best car for the current GT3 “class” in the game is? My usual pair of the M8 and Corvette that I raced are out now as choices.
Really, the GTE/old GT2 cars were pretty balanced before, Viper needed a tire width nerf front and back, C8R needed a front tire with nerf. Ferrari needed a rebuild for more grip and a power nerf (554 was about perfect). M6 needed a bit more power/grip, but not much. Only outlier was really the 15 Porsche which was really, really bad and improssible to balance with build.
The reworked builds aren’t bad. They nerfed all the cars grip down close to the 15 Porsche, and it still needed an artifical grip buff. C8R is weird because it’s so slow in the straights, but a grip monster. Ferrari still weak on grip, Ford GT power nerfed for no reason. The power of the 17 Porsche was underestimated. Basically they made balancing harder than it needed to be by starting over on builds.
If we are going for the accuracy the Ferrari 488 shouldn’t be in gt3 at all. It only races against other 488 challenges in the spec Ferrari challenge series
Technically neither should the 935 Porsche (although at least that feels like it has been nerfed from the rocket-sled that it was previously) and both the Super Trofeo Lambos
If we want to get really technical the first gt3 cars and rules where deisgned to include all these cup and challenge cars, the very first races saw lots of cup porsches and challenge ferrari stradales altough manufacturer’s quickly made aero kits and wider tyres to add to the cup cars to make them conpetitive with the new home grown gt3 cars like the r8, sls and db9 gt3 that joined in the first year or 2.
What constitutes “GT3” class or many others, has had so many variations and permutations over the years you could fill a library of books up about it.
Oh I’ve got no problem with them being in there, just highlighting the pedantry.
The 935 is still an odd-ball though, it’s basically a GT2 RS with an aero bodykit and srtipped race interior so should really go in to Modern Factory Racecars with the SCV12.