I use bluetooth headphones and have occasionally experienced the stuttering even without wifi active. My fix when it happens is to turn bluetooth off then back on again, I suggest you try that need time you get that problem. I haven't yet applied this patch so I can't comment on whether it makes any difference to the problems the N900 already has with bluetooth.

Bluetooth and wifi both use the 2.4GHz frequency range, and apparently the N900 uses the same antenna for both of them, this seems to sometimes cause interference issues between them.