128 bit vs 256 bit

Here are two same Geforce GT440 models
1:512mb of GDDR5
2:1gb of DDR3

gddr5vsddr3.png


for further details visit http://www.hardwaresecrets.com/printpage/GeForce-GT-440-512-MB-GDDR5-vs-1-GB-DDR3-Video-Card-Review/1272
 
if you want to know which graphics RAM is faster
6750 have 128bit with 4600mhz DDR5 the memory bandwidth of this card is 134.4GB/s
GTS 250 have 256bit with 2000 DDR3 the memory bandwidth of this card is 128GB/s
so 6750 have faster memory bandwidth and a little faster on games and it support DX11
GTS250 support DX10 so it cant enable some DX11 games effects .
 
the bits are bandwidth. you have less lanes going to your memory with 128bits, but the ddr5 ram really compensates for it.

therefore, as oxford said, they have pretty much upgraded you 😛