Obviously you never played the demo, which has HUGE improvements over 5. And are you seriously suggesting a current-gen racer should be able to solidly compete with a next gen machine with tons more power.
I've yet to find "huge" improvements. Steps in the right direction, sure, and I should spend more time with it, but even as is, the GT6 demo, at least to me, offers nothing in the physics department I don't already get in FM4, to say nothing of what FM5 might offer.
It's good to read the "but the other game is on a more powerful system" excuse now, and get used to it, since it's going to be used
a lot come the fall. The 360 wasn't as strong in many ways as the PS3, but I didn't see people lining up to give it some leeway. Yes, the gap between the new-gen and the PS3 is bigger, but the fact of the matter is these are two racing games coming out near the same time. Simply because one team chose to stay with the old gen does not give them a pass - if you want to look at it another way, their game should absolutely be more polished, since it's not an exploratory splash in the new-territory wading pool.
GT5 got mediocre reviews? Not sure what you were reading.
Metacritic has it as the lowest full-iteration home console title in the series. Prologue is just slightly under it, and the PSP game below that. The FM series is consistently ranked higher than its contemporary GT rival. Though, taking the five main GT titles versus the four FM ones, GT does slightly hold and edge with a 91.4 average versus 91.25. I'd hate to bet against that edge being the same by the end of this year...
When did Forza work with KW suspension and Yokohama tyres? Again graphics? You can't compare next gen to current gen, and GT6 looks amazing for the outdated hardware it is on. (Also going to say the new Forza does look nice)
They worked with Pirelli to quite excellent results in FM4, for one.
As I said above, you absolutely can; they're coming out on the same date, so as much as certain people don't want the comparison to take place for their own preferences sake, it can and will happen.
Also, amazing versus nice. Heh.