Hello there. Welcome to the forums.
Actually the model of the iPhone has nothing to do with the fact that it can or can't synchronize your outlook calendar and contacts, because they run on the same iOS 4.2.1 Build 8C148.
The main difference on both iPhones is hardware related.
Here you have a Comparison Chart between the iPhone 3GS and the iPhone 4 Apple - iPhone - Compare iPhone 4 and iPhone 3GS
Check it out and hopefully that'll help you make your decision
Post back your results EDIT:
answering directly your question. yes, both iPhones will be able to synchronize your Outlook Calendar and Contacts, you can read it more explained here: How to Sync an iPhone With Your Outlook Calendar or Google Calendar | eHow.com