Assuming standard clocks, GTS250 > 9800GTX+ > 8800GTX > 9800GTX > 8800GTS (512MB/G92 GTS) > 9800GT = 8800GT. The problem is all those cards 8800GTS and up are all the same card. The 8800GTX is slightly different due to the memory bandwidth but the GPU part is the same. The only thing different about them is the clock speeds. The 9800GT is the same as the 8800GT. Its on a smaller die so its either clocked a bit higher, or more energy efficient. They both have the same 112 shaders and are identical.
8800 GTS with 786MBs of ram? Sure its not the GTX? If its the 8800GTX, thats the best performing card. The 9800GT isn't far behind and if you have a weaker PSU might be your card. A $50 Geforce doesn't tell us a lot, but its probably junk.