asterisk users - Jun 2006 - Will 200KB/s drive access be OK for voicemail storage?

I'm using a Linksys WRT54G router and it works great but it only has
4MB of storage.  One of my only options is to modify the router to
accept SD cards (eg. 512MB) but the access time is only around 200
KB/s.

Will this be fast enough to store voicemails?   ...or do I need
another (faster) storage device?