This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
The answer is it depends. You should strip the STS part out of the question and post in the perfomance forum for a better discussion on the topic. If your goal is to throw more memory and larger heaps at STS than yes a 32bit version will restrict that.