These upgrade cards, their speeds, the differences between them, etc. is probably the most well documented of the powerbook upgrades out there.

Compares Sonnet's upgrade cards:

http://macspeedzone.com/archive/5.0/bymac/app/PBK14_166Oct00.html

User experiences on the Vimage - note the reports of increased heat and decreased battery life:

http://forums.xlr8yourmac.com/action.lasso?-search