Would a 650ti be better than a 560ti? That's the card my brother had, until it broke (physically)
I know the 550ti was severely gimped compared to the 560ti
Where the 550Ti was gimped compared to the 560Ti was in two areas - bandwidth and CUDA core/ROP count. Both are areas where even the "gimped" GTX550Ti trumps the non-Ti GTX650.
Think - the GTX550Ti is a cut-down GTX560Ti; naturally it would be gimped compared to the more-expensive relation. (The same is true comparing the GTX650 to the GTX660 - either non-Ti vs. non-Ti OR Ti vs.Ti.)
By rights the GTX550Ti should be compared to the GTX650 non-Ti - they are priced identically pretty much for the same memory loadouts, and have similar power requirements; however, the Fermi part has higher bandwidth than the Kepler part (192-bit memory bus for Fermi vs. 128-bit for Kepler).
Given identical RAM configurations, bandwidth needs of your games should rightly determine which you should buy (especially since, as I pointed out, GTX550Ti is directly price-comparable to GTX650 non-Ti).
The same is, of course, true on the AMD side of GPU Street (HD7770 vs. HD7850 or even HD7850 vs. HD7870) - in the case of the former, the HD7770 has a bandwidth disadvantage compared to HD7850; however, it makes up for it with both lower power requirements and a lower price - the latter two are identical in terms of bandwidth, but dissimilar in terms of power draw and (again) price; still there is a smaller gap there between HD7850 and HD7870 compared to HD7770 vs. HD7850.
HD7770 competes with both the GTX650 non-Ti and GTX550Ti in terms of price and RAM loadout (except that 2GB loadouts of HD7770 are not common among AMD AIBs, while both GTX550Ti and GTX650 non-Ti have a plethora of 2GB iterations from nVidia AIBs) - If you are looking in that $100USD-$200USD (single GPU) price range and don't have loyalty to a particular GPU AIB or even AMD vs. nVidia in general, it can be rather difficult choosing a card.
Normally, I stick with AMD (and ATI before that) - I have NEVER purchased an nVidia GPU for my own use. However, the higher bandwidth of the GTX550Ti - at either the same price, or even a bit cheaper, compared to the HD7770 - has me rethinking that.