Thanks for responding. Upgrading from 7.1 to 7.7 added the i.a. Instant Replay on the Preview page and a.o. new menu items on the Setup pages. PC's are Core Duo on Intel 965 MB and Pentium D's on Intel D945 MB and D915 MB's. Checking the Processor's/Memory Performance under Task Manager did not reveal anything unusual or major differences.
Reinstalling 7.1 improved the smoothness on Preview noticeably and breaks in movement are less sharply defined. I'd really appreciate Avermedia providing info as to what the Preview fps should be, or what it is spec'd at? Our local Avers Rep referred to Preview as being realtime and was surprised that we weren't achieving it, but did mention that 'older' systems presented problems with upgrades beyond ver 5.5 or so. We've never seen realtime preview on any of our NV3000 or NV5000 installations and weren't expecting it either but with 7.7 it really becomes a problem.