It''s my understnading that there is little, if any difference between VC Offshore and Baltoplate, except for color choices. This could be misinformation, but I heard it from several reliable sources (none of whom was Interlux, however).
Last spring we stripped 17 years worth of ablative paint off of my C&C 37, then sanded and painted with Baltoplate over blue VC (to get a "tell" layer when we sanded). Unfortunately the yard had to machine wet sand it with about 400 grit for us since they were SO late getting the job done, and we did not have the chance to hand sand before the season.
However, between adding new sails (Pentex 150, Dacron Main) and a new bottom, it was like sailing a different boat. My crew was utterly novice this year and last, and we went from finishing 15-20 minutes behind the fleet to generally finishing with the fleet (except light wind nights - but that''s another issue), even beating out a few boats every now and then. It doesn''t SOUND like much, but you can tell the difference between last by :30 and last by 27:30.
Also - one thing I noticed with the new bottom - the boat coasted considerably farther in neutral. Almost proof positive that she''s moving through the water better from what I can tell. We probably coasted at least twice as far this season when we dropped out of gear.
Note - I had a diver come every week. Baltoplate/VC, where we are in the Northeast buys you less than two weeks before the slime starts to accumulate. A diver is needed at a minumum bi-weekly to keep the crud off. So if you don''t want to have someone dive or do it yourself, it''s not great. If you are planning to wet sand it and then keep it clean it would seem to make a difference.