This will clear everything.
First the shaders cores GTX 650 have 384 cores while GTX 550 Ti has only 192 - Shaders cores doesn't really matter since AMD have much more shader cores then nvidia.
Texture Units They are very important but because both have 32 units we will skip this.
Color ROPs they are same too so i will skip it too.
Core (Shader) Clock it is very important lets see this section:GTX 650's core speed is 1058 MHz while GTX 550 Ti's 900 (1800) MHz but ignore the shader clocks(Which are in brackets) because as i said shaders don't really matter, so here you can see GTX 650 is winning, with 2 points
Now the Mem bus here GTX 650 loses(128bit - GTX 650 and 192 - GTX 550 TI)
Memory Bandwidth - GTX 650 loses here too(80 GB/s Vs 98.5) so it is 2-2
now Ram - important to know that the 'G'DDR is better then DDR but here an tie so 2-2
Now Maximum Thermal Design Power - It is important so i am going to extend this one.
- Okay while GTX 650 uses only 64 W and GTX 550 TI uses 116 W
- So if the OP have an low power PSU then he don't need to upgrade it, means less expensive if you have an 450W PSU then it is enough for GTX 650 while GTX 550 Ti needs 500W PSU so the OP don't have to upgrade his PSU to install this card.
- Also you save money everyday with an low power use
- GTX 650 = 3 Vs. GTX 550 Ti = 2
Now price - GTX 650's price is 109 $ while GTX 550 Ti's is 110-130$ so one more point for GTX 650 it is 4 Vs. 2
Now how you were telling that GTX 550 Ti is better then GTX 650? prove it make an post like this one and prove that you are right, I have 2 yrs experience in this type of things, if i am wrong then i have alot more to learn.