I've owned a 7ECA with the O-200 for three years now. I bought it to have to fly while building the Bearhawk Patrol, and because it was light enough that I could fit my oversized butt and a 200-lb instructor (is there any other kind?) and still have UL to carry enough fuel to do some useful training. Empty weight is 1027, max gross is 1650, so I've got 623 lbs of UL.
At gross weight, we see about 200-300 fpm (bumpy air) on hot summer days at near sea level (DA ~ 4000'). Solo, I see closer to 350-400 fpm. Cruise at 5000 ft and 2400 rpm is about 85 mph. Turning 2500 rpm gets about 88-90 mph. Running 2600 rpm gets me about 92-93 mph, and 2700 rpm gets about 94-95 mph. Diminishing returns as you add power / increase fuel consumption. And ALL of those numbers are substantially lower than my performance estimates for a "new" 7ECA with O-200. (I started with the O-235's "book" numbers, and used standard aviation rules of thumb to calculate revised "book" numbers, since there is absolutely no operator's manual, pilot's guide, or any other documentation for the Continental powered 7ECAs...)
But then, my lower-than-book numbers make sense, because my prop has been "worked on" quite a bit. While it's still (barely) airworthy, it is absolutely NOT as efficient as a new one would be. I'd love to replace it with a more modern profile propeller, but McCauley no longer sells the specified propeller, and the O-200 model 7ECA has no STC'ed props available that I can find, and my IA is hesitant reluctant to sign it off if I replaced it with one of Sensenich's newer wood props, even though the TCDS says "Any other approved fixed pitch wood propeller which is eligible for the engine power and speed and which meets the diameter and static rpm limits specified under 'Propeller Limits' for the pertinent model." I suspect I'd be a LOT happier with a Sensenich than with the ancient McCauley 1A100ACM69 in its current condition!
Given all of the above, and if I were given the chance again, I would still buy the plane. I've learned a lot flying it, and it's a lot of fun to fly. And best of all, it's cheap to keep, and cheap to fly, and insurance is very affordable.