Yes there is quite a bit of difference. Those numbers you listed are the width of the memory interface which determines how many bits can be transfered per memory clock cycle. More bits = more data which usually = better performance. Though higher bits doesn't always mean higher performance. An old example of this was a Geforce 6800(256bit @ 300mhz) vs a Geforce 6600GT(128bits @ 600mhz). They both effectively had the same memory bandwidth and similar performance since the 6600GT had half the bus, but cycled twice as fast.
You do not want to get a card with a 128bit bus if you want good performance in modern/upcoming games. Usually you'll only find them on neutered cards. Aim for 192+ bit. Look for either nVidia 8800GS, 9600GT or 8800GT or AMD/ATI 3850 or 3870 cards.