Moroso 89650 power speed calculator or "dream wheel" is a handy item. I have a few laying around here. Mark Williams also does a nice one. wallaceracing/calculators are good if you have the internet handy.

Converter loss is one of those things you sort of figure out once the car's together. Speed-tire size-gear ratios should calculate to a RPM number. If it's off, something is slipping. A few hundred RPM is normal for a torque converter. I've seen some cheapy, poorly speced or broken converters slip a lot more.