No, the savage is not much bigger than the revo. Yes, with the stock savage tires it has that appearance. Here is a pic for comparison.
Both trucks are really good. The Revo has been trouble free for me, and i feel its overall quality is higher than the savage. The savage is great, and HPI is an awesome company. They now sell the diff upgrade, which is relatively cheap. Thats really a win-win situation. You just cant lose. Both companies are among the best in the biz, and are currently selling the best trucks. Flip a coin. I prefer the Revo though. As for the fuel, buy whats available to you. Or give us a list of whats available, and we can tell you what we think is the better option.