Taken care of, most engines should easily last more than five gallons. I buy mostly the cheap Taiwanese engines - and am totally happy with them btw - , and they seem to get a solid eight-ish gallons or so. They never cost more than $150, and do their job well. With the more expensive engines, you can do more maintenance-type stuff on them over time - change conrods and bearings, etc.., and get ten+ easily.. I like the cheap SH engines 1.) cuz they're cheap, 2.) they run well, 3.) if something goes wrong and I ruin an engine, well, it's not like I spent - and therefore risked - a fortune on it.., and 4.) they're just very user-friendly, not too picky to tune, match pipes and plugs with, etc.. Run one for eight gallons then buy another one.. Easy.. Also, having 3-4 RC's to keep running makes me tend to the cheaper engines. For the most part, the price difference isn't worth the performance difference from cheap to expensive engines, IMO. At least performance that I really need(12 minute run times for ex.. Who needs that except the most serious racers?..)

In any event, most nitro engines should make eight gallons easily if you take care of them, don't run them too lean, etc.. Eight gallons is a lot of fuel. I have several RC's and twice as many engines, and I've had eight gallons take two years for a couple of them..(OK, due to work, weather, other commitments, etc.. I can't run nearly as much as I'd like.., but still..)

If you get for ex an OS 28 or OS 25XZ for your RC8T, and don't run it like a bonehead, you should get eight gallons without worries.. (I'm considering one of those engines for my SC8 btw, but am really looking for a killer deal...)

If you have no experience with nitro, get a cheap SH engine to learn on, and something "better" later once you've got the hang of things..(you can get a Losi 454 out of an 8T 2.0 for cheap on e-bay.. Will easily overpower your truggy - good for bashing... Just a bit thirsty for competitive racing..)

For mindless plug-and-play, go electric.. I don't find it nearly as exciting though.. But hey, some people like it, so whatever - to each his own...