I was recently looking at new graphics cards for my computer and was wondering is there that much of a difference if I get a card with a 320-bit (or higher) memory interface to a card with a 256-bit memory interface?
More about :memory interface difference graphics cards
Just means higher memory bandwidth. If the bandwidth is high enough already (which it will be if it's gddr5), the extra few bits won't make much of a difference.
By the way, what cards are you looking at?
Don't stare yourself blind on any one spec, but instead you should read reviews.
There are so many variables (shaders, clock speeds, memory bus, memory type, transistors etc.) that you cannot decide which card is better just by one single specification.
A 320 bit bus wont be much of a use if the rest of the specs are crappy.
The articles here on toms is a good way to decide which card to get:
MSI 790fx-gd70 MB
AMD 955 Black Edition Phenom II X4 @ 3.2GHz
Kingwin Mach 1 1000W PSU
4gb OCZ Black Edition DDR3 RAM
Going to be getting a 600GB Velociraptor HDD (cause current HDD is horrible)
Windows 7 64-bit Home Premium