RE: Super Tigre 2300 or 3250 ??
First off, what size engine is recommended by the maker of your model airplane? We'd stick within that.
When you're asking about "the new carb", we're not sure what you are asking.
Propeller choice will be dictated by the model's size, weight, and what engine you wind up using. The G3250 would normally be run in the high-7,000's, The G2300 should be run in the mid-8,000's. They should be propped accordingly, but we don't have any listing for a 3-bladed prop.