It will probably be happier with 10° or more. The vacuum should rise with more timing. I guess I can't say that for sure. I haven't paid attention to that. When you advance your base timing you will probably have to limit your total timing (at 2000+ rpm) by modifying your distributor. This whole thing can gat a bit complicated. That's why most people just find a happy medium and as long as it runs good, doesn't kick back against the starter (from too much advance) and doesn't ping, all is good.