Worth it, and I don't know why mr.pro gamer there bring us the 'hw compare' site, which is not really reliable for comparing GPU's. It's just comparing by texel rate and pixel rate and other specification which is not really reliable. Anyway 6770 is in the middle between GTS 450 and GTX 550 ti, so it would be like: GTS 450 = HD 6750 < HD 6770 < GTX 550 ti = HD 6790. You can see the difference between the 6770, that the 6770 is a faster card. So I think it's worth it for just a $6 increase.
And I think you are wrong on ''physx which is applicable to many games..'' because there is no much games that supports Physx Actually. Here is a list: http://en.wikipedia.org/wiki/PhysX
You can see that it's pretty few games that supports PhysX.
Hope this helps and have a good day