oh god, can't believe i'm gonna post on this shit.... i'll just say my thoughts.. I could give two shits about each.. I can't play a racing sim for more than five minutes without rather scratching my balls... I've had all the Forzas, and i have GT5P d/l on the absolute bottom of my DL list on the XMB. they all bore the hell out of me.
GT5 has the better car models. It just does... god,, there's no amount of spinning to negate it.
GT5 has better lighting and shadows (the whole reason it has more of a 'real life" aspect)
FM3 has better textures on the tracks and environment., and better physics/collision when i see the vids.
When i see these side by sides of the mountains, even though the forza track has more textures, the shadowing on each individual craggy part of GT5's mts give it a more realistic look, even if less dynamic in geometry.. It's more of a point light source, where FM3 is a box light source... and it just gives a better feel for realism.
Apparently shadows are HUGE in providing realism b/c i couldn't put my finger on it for the longest time, until i scrutinized it... When one little jutting on a little ridge in the Alps has a shadow on GT5, and a similar jutting in a different locale doesn't in Forza,,, it just looks a bit more arcadey in comparison...
I would take the realism effect over arcadey, jmo. I do like the feel of forza better, but, GT5P never felt finished either, so, i'll have to wait to call it..