If you have the extra money, go as fast as you can. In case you have not ever read it, the best\cheapest way to order the 2.8, is to actually start your order for the 2.4 24" and "upgrade" the proc to 2.8. This allows you to keep the ram at 1GB, and order what you need, max 4GB, elsewhere, say Crucial or OWC, and save literally hundreds on ram alone.
Play around with the configurator on the Apple site and you will get the idea.