I think you owe it to JV partners to split test with your own leads... if you don;t have a list, build one with PPC, ezine ads, or some other rapid traffic source... and warm them up with some email copy before sending cold traffic to your sales page (and you can be split testing your lead page too)...

i guess you could try to convince someone to do a test mailing to their list, but I'd think you might want to offer them some sort of incentive for doing so (like a higher percentage of profits)...

if you're planning a launch, you can do your split testing while recruiting JV partners for a syndicated launch...just make sure your results are in before your pre-lanch so you can release the numbers...but it at least allows you to run tasks in parallel reducing the wait for your syndicated launch...