Tuning with jets, Power valves and an O2 guage

I have the initial timing set at 19* with a total of 33 degrees. I have it idling at 1000 rpms. I've heard to set the initial at a point where I get the highest manifold vacuum, but that seems odd to me. What if I run it up to 25 degrees? Wouldn't it be hard to crank over then? Of course if I set it to 25 degrees initial, I'd have to modify the distributor to limit it to 33-34 degrees total. I guess I'll need to learn how to do that!