Running Froyo on legend (vodafone branded) and have the same problem of lag, battery drain etc...
if u turn off the background sync, then the phone does become bearable, but still the phone drains the battery like anything... a 10min call drains more than 10% of the battery...
some people also claim that it does get better after enabling the USB debug mode (Settings > Applications > Development)...
found this to be somewhat relevant:
HTC Legend - post FroYo - 100% CPU issue (more tha... - Vodafone eForum