It's likely that very few people here play GP4, so that may well be why you haven't received many replies to your inquiry.
GP3-2k has very slightly better AI than GP3, debris collision damage, and somewhat better damage. GP3 has probably somewhere in the rough vicinity of a dozen times as many carsets and carshapes as GP3-2k.
The original GP3-2k tracks are fairly detailed. The original GP3 tracks are considerably less detailed. GP3/GP3-2k addon tracks are mostly very detailed, often considerably more so than the original GP3-2k tracks, and I would say that they very often compare favorably with the original GP4 tracks. Almost all GP3-2k tracks will work in GP3.
GP3 is considerably easier to edit than GP3-2k.
That's it, in a small nutshell, GP3/GP3-2k comparison-wise. There have been threads in this forum with much more extensive and detailed comparisons between the two games. You should be able to find them with the forum search function.
GP4 has somewhat better AI than GP3-2k, although it does seem to me that the GP4 AI do spin off just a little bit too unrealistically often.
It has generally marginally more accurate tracks than the better addon GP3/GP3-2k tracks.
It seems to use essentially the very same physics engine with simply different values, as GP3 physics files are usable in GP4 with GPxPatch.
GP3 has lovely addon menu artwork and menu backgrounds, as opposed to the dark little ones in GP4. (No offence meant to the few that have made GP4 backgrounds, but it's just a limitation of the game.)
Edited 1 time(s). Last edit at 04/18/2004 12:03PM by JackiMatra.