I don't think he's looking to fly military fighters. Nobody sustains 7-9G in any piston plane, aerobatics or not. The Unlimited monoplanes might pull G is this range, but it'll only last about 1 second. There's no need to pull more than about 4.5G at the Sportsman level. And even at that, the G is experienced for very short amounts of time. You really don't have to be in great shape to fly aerobatics, or even competition acro. If you came to a contest you might be surprised that many guys have the same beer guts that non-acro guys have. :-)
Oh, I know. I know a lot of military pilots who are rather flabby too. The point is not the actual level of fitness but the cardiac issues that tend to lurk asymptomatically in those of us with a sedentary lifestyle. I agree that there's no need to pull more than 4.5 g but would say that it extends beyond the sportsman level to include any level to be quite honest unless you're in combat. You get much beyond 5 or 6 g, especially if you're inverted and most people are going to find it downright unpleasant. Even with my masochistic streak, this is the case with me and with most of the folks I know who do aerobatics. I just don't see the need to do anything beyond that but then again, I tend to look at aerobatics and such at airshows like Oshkosh with a healthy degree of "Eh...that's nice....moving on". My point about the RV series being unsuited was from the assumption that he had little background in aerobatics and was looking to go out and really tear it up. Even for 4.5 g, a marginal factor of safety of 25% would put the RV series at the lower end of the suitability spectrum and I wouldn't go beyond that level in an aircraft without a much higher design load tolerance.