Why the devil would any self-aware racing sim fans be comparing GT5 and Forza 4? Both have comparably good racing physics, but the AI on Forza is too far on the arcade side of things to call it a sim (for single-player - obviously they're both effective sims on MP). When you see cars regularly shooting off corners (every 3-5 laps), being able to go from 8th to 1st in half a lap early on and having the AI cars blatantly ignore the laws of physics, it's just not possible to call Forza a racing sim (again, unless they release an online-only version). GT5's AI has its flaws, but if you watch a replay of a race of GT5, it looks very similar to watching real motorsports. Forza, on the other hand, is like watching a highlights reel, which is not a reflection of a whole race, but rather just cherry-picks the 'exciting' bits. Both are great games, but both are very _different_ games. If you want unrealistic action with realistic physics, go for Forza, if you want the best the consoles have to a non-F1 motorsports sim, go GT5.