Every time this question comes up someone posts the following list:
Maybe a little biased but the 7 has many advantages:
1) 50% Stronger airframe (+6 to -3 g vs +4 to -2)
2) Higher Vne (230 mph vs 210)
3) Higher maneuvering speed (142 vs 118)
4) More fuel (42 gal vs 36)
5) ~5 mph faster on the same engine (160 hp)
6) Slightly higher gross weight (1800 vs 1750)
...
Costs the same to build either one.
1) While true, if you are worried about +4/-2, then don't ever get in a Cessna, Piper, or many other certified airplanes.
2) Not an issue. Even with the O-360 in my -9, I can't hit 210 mph. Going downhill, you will want to throttle back (with a FP prop) to keep from over speeding the engine.
3) Not an issue. If you ever have to go full and abrupt control inputs in an RV, any RV, something is seriously wrong.
4) Yep, only 36 gallons but then you are running a smaller engine than an RV-7, so you don't need the extra fuel. (Even with my O-360, I can fly for three plus hours and still land with an hours reserve and a full bladder.)
5) It is more like 3 mph according to Van's web site. Call it the same speed.
6) Yep, the -7 has a higher GW than the -9 but then the -7's typically have a larger engine that often spin a CS prop so their empty weights tend to be higher.
Let me add:
7) Takeoff distance. At gross, the 160 hp RV-9 will be off the ground in 475 FT and land in 450 ft. A 200 HP RV-7 will require 500 feet to get off the ground and will need 500 feet to get back on the ground. A 160 HP RV-7 will take 650 feet to get off the ground.
8) ROC. Both 160 hp versions of the aircraft in question will climb at 1400 FPM at gross weight but the -9 has a higher ceiling.
Now back to the real world...
All of those numbers are so close and can be controlled by the builder and the pilot that they are virtually identical.
Buy / Build the plane you want for the mission you want and you won?t be disappointed.