Will the features of gt300 equal to that of 5870? Or there are other advantages of gt300 over 5870?
It is easy to speculate that the GT300 would be faster, but the only question would be when?
You really shouldn't worry much, we don't have a looming 'Crysis-like PC-killer game' on the horizon. Most games have been pretty much limited to what could run on the 360/PS3, there's just usually a little more detail on the PC version.