I'd go with the 240 also. Here are my reasons:
1. Sure on the 225, 3 feet back is great, but I'm not sure how well you will be able to take advantage of those 3 feet, being that the aquarium is only 24 inches tall. Plus it's acrylic anyways, easy to scuff up.
2. The 8 foot long tank would be really impressive based on the fact that in the 8 foot span, you could have enormous variation in your aquascaping. IE you could incorporate the fruit stand thing, the cove thing, the rock wall thing and the piller thing all in one aquarium no problem. And 2 feet back? Thats plenty.
3. If you are going to jump on the T5 bandwagon, you could just do two 48 inch fixtures, the most cost effective T5 length. This would also make aquarium maintenance easier, because you could just take off one of the fixtures PRN.