a r32 with a full tank of fuel weighs the same as r33 with a nearly empty tank. they are 4% heavier, but have over 20% more power.
but yes, an rb25 is a much better place to start. a guy in town just spent $8000 doing up an rb20. he put a stupidly big turbo on. he makes full boost at 5800rpm, and his redline is at 7200rpm. max power is just under 250hp (~185kw), and off boost it is hopeless. now for a darn sight less than $8000 he could've bolted a stock rb25 in and made the same power and had a much nice car to drive.