You will get lots of different answers---but you will need to know a little bit of info behind each answer.
1. Rate of climb is highly dependent on engine size and aircraft weight (actually gross weight at time of test).
2. Speed at various rpm and alt. A couple of speeds at a couple of rpms at one altitude should be enough. However, you will probably need to know what the engine is (type, HP, perf mods like hi-comp pistons/port/polish etc), the propellor type, pitch, and diameter. You will also get lots of variance in the airspeeds even with like weight and power due to builder attention to drag. Paying attention to drag adds up faster in speed mods than HP additions.
3. GPH is good to get but you will also want to know if they are running with electronic ignition and fuel injection. The data is also meaningless unless you how many degrees off peak (and in what direction) you are running the engine. Not everyone runs with a fuel flow gauge, so you may not get great info.
4. Weight. You will need to get a feel for what they have on board like full IFR, night and the kitchen sink. On my longez, I was carrying a good amount of lead in the nose (big engine, light pilot, short nose).
Aircraft drag details (wheel pants, gear fairings, spinner, other special contours)
Engine carb/fuel injection/throttle body
Engine inlet (updraft/downdraft, NACA, P-51, armpit, etc)
Prop type, pitch, diameter
gross wt at test
OAT at test
altitude at test (set 29.92)
speed check on 2 rpm settings at same alt
gph at each rpm setting along with degrees off peak and which direction
But then again, maybe you are just looking for anecdotal information. In that case, my Longez climbed over 2000 ft per minute light loaded with only me in the cockpit. Heavily loaded, I placed the throttle to wherever 176 mph IAS was at any altitude up to 10,000 ft. Don't have fuel flow to give you---but ran at 100 deg ROP. My engine was a Lyc 0320 EXP, ported and polished with 10-1 compression turning a Herzler Silver Bullet. I was on the draggy side. But I did have downdraft cooling (pressure plenums), carbureted, wheel pants with no fairings