The answer to that is how many electrical items will you have running?
With 30 amps you won't be able to run more than 1 element of either 4500w or 5500w at a time. Were you planning something different? How big are you planning for your RIMS element?
We really need to see what you are planning to do so we can get the full picture. Then other decisions can be made. Electric brewing on 30 amps is completely possible. With a RIMS, that's a little bit tougher. With a HERMS, aka Kal's theelectricbrewery, it's a bit easier.
4500w uses 18.75 amps
5500w uses 23 amps
Watts / voltage = amps
Pumps use probably an amp at most.