I'm actually with bruce on this. The cards perform close to each other, its pointless to spend more for one. (unless you really want to have the next level of DX now.) Let me show you what I mean.
http://www.hardocp.com/article/2009/11/10/need_for_speed_shift_gameplay_performance_iq/4
Scroll down to the bottom, how does the 5750 compare to the GTS250? Same settings, basically the same scores, the 5750 comes out .1FPS faster on average.
I guess I'll show Borderlands for the GTS250 win.
http://www.hardocp.com/article/2009/11/30/borderlands_gameplay_performance_iq/5
This is the first resolution where one of the cards at least has everything on, and its the GTS250. Not only that, its faster to. Looking at other benchmarks the 5770 is a closer match to the GTX250, but the 5750 can keep up in some games.
There is so far one game out that truly can use PhysX. DX11 is new and probably RIGHT NOW doesn't have one. I refuse to believe for one moment that there will be more DX9+10 games using PhysX then there will be DX11 games. There will continue to be games here and there that use it well, but there will be plenty more DX11 games.
Troll talked about Tessellation bring the 5970to its knees, PhysX can do that as well. Take a look at this.
http://www.hardocp.com/article/2009/10/19/batman_arkham_asylum_physx_gameplay_review/9
At 2560x1600 with 4AA and PhysX at max, look what happens when you outside. Frame rates are nearly always under 30FPS, with a lot spent in the 21FPS and 6FPS range. Tessellation might be the same way. If you turn it up, it will choke. (again, similar to AA.) Hard also had this to say from the review.
http://www.hardocp.com/article/2009/11/06/unigine_heaven_benchmark_dx11_tessellation/
While this Heaven Benchmark application isn’t an actual game, it does give us a glimpse of how Tessellation might be used in games. If used in this manner the benefits can be quite noticeable and greatly improve the gaming experience. There is a performance penalty for enabling it, as the creation of geometry on the fly does not come free...maybe we will see user adjustable controls that could allow us to vary the level of Tessellation depending on the user’s GPU abilities like much of the other eye candy we see in games.
Or in other words just because you saw something on youtube doesn't mean its going to end up that way.