alright dude, here's the deal: bigger is not always better. Some people will say otherwise, but I have a dyno test book showing otherwise. On a stock motor w/ an X303 cam, ported dart heads, gt 40 upper, 24 lb injectors, pro m 77 mm MAF, 1 5/8 shorty headers, h-pipe, flowmasters and crane 1.7 roller rockers, the 70 mm actually had LESS horsepower than the 65 mm. It only made 1 less hp than 70, but it only made 1 more than stock, so i'd say if you're doing this upgrade to make horsepower, it's not the greatest idea; if you need a new throttle body for some reason, 65 mm would be good probably even better. I have a blown 306 that should be making around 425-445 hp at the crank and my TB is 65 mm. I'm not saying I have any experience with this, but dyno tests don't lie.