I don’t have the appropriate cards to be able to test it myself, but it should be a very noticable difference. Especially when copying content to the card. Class 6 is so cheap right now, I wouldn’t consider Class 4.
Newegg has 4GB Class 6 cards for $17 shipped and 8GB Class 6 cards for $37 shipped. At those prices I don’t think the few bucks you’ll save on Class 4 justifies the performance penalty.
Actually a 4gb class 4 isn’t that slow or different.
I have a 4gb Fuze. I just tried my 4gb card with 2 new songs and they synced using WMP10 as quickly as others, loaded just as quickly after I disconnected, and using Recently Added feature, they played right away. Maybe because mine’s a SanDisk card? It does have the 4 in a circle in the upper right hand corner of the card, so I know it’s a 4. I do have a bunch of podcasts on there (put my learning spanish on one disk)… it says 3.37gb left on the card… so maybe because it’s not full it was faster? My podcasts also play immediately.
I didn’t know about the classes when I bought them so I just bought them off Amazon, they were less then $10, about $15 with shipping… Now I think I’d probably look for class 6 if they have them but I don’t see much difference in mine with the 2gb, which is full and I have no idea what class (doesn’t say and I no longer have the packaging) or my internal memory.
REFRESH, turned it on and turned it off and trying the cards I have… Just put my 2gb in and it took less then 30 seconds to refresh (this one is almost full). Now I’ll try the 4gb… took about 12 seconds (with the little bit I have on it).