They are both great airplanes... if elbow room is an issue for you with the 7, just check the dimensions (I think the website has cabin dimensions listed), set up two chairs at the distance specified, and see how you fit.
Or better yet, find a 7 and an 8 you can sit in... or take a ride in. It is
very unlikely that an RV owner would
not be willing to take you for a ride if you mention that you're thinking of building one. ;D
The only one I've flown in is the 4, and it is a bit tight for sure. Also there is a strict limit for rear-seater weight... I think the 8 has a little more headroom, but the width is about the same. Not sure about the rear seat weigh limit on that one.
But if you get a ride, you may feel that being a little cramped is a small price to pay... they are just so much fun to fly!! And versatile, performance-wise... the 4, for example, is great for screaming along at 10,000 feet at about 200 kts (you can actually exceed Vne in level flight in the 4), but you can also show up the Cessna drivers by cruising with power way back for fuel consumption of about 5 gph with a still-impressive cruise speed of about 130 kts. They are also well-behaved in the pattern, with flaps that work very well. Not a beginners' airplane, really, but not so touchy that people haven't used them as a first airplane. RVs are probably the most successful kit series ever, well-supported and well-proven. I hear they are getting easier to build, too, which is good, because it's not an "easy" project like a Sonex or whatever.
The bottom line is that there is really nothing comparable, in terms of price, operational cost, and performance, that will give you more interior room or baggage capacity. If that is a priority, you need to look at the "utility" designs that trade speed for all that stuff, I guess.