It depends on the combination , a lot of race cars have no curve , they set the timing at 36* - 38* & that is it , most have a start retard to get the engine running & as soon as the starter circuit is released it returns to 38* .
for street use you can have a lot of initial timing & yes vacuum will rise usually RPM also but past 20* it will usually get grumpy about starting easily the other thing that happens is you need to get inside the dist & modify the slots [I weld them] so the curve doesn't exceed 38* with RPM