Regarding ergals:
I weighed 175 when I was very lean, quite fit, and a decent sprinter. I rode quite a few ergals, mostly on the front, but on the rear for light wheelsets. 28 fronts, 32 rears. Red label rear, yellow front, 32's, was a typical training set for me.
Never had a problem, loved them, and also found them to have a mysteriously sweet ride. Maybe I just made that part up.
Heavy as I was/am, I've always been able to ride light wheels. I've got a very light set of Araya aeros, which were quite prone to cracking at the spoke holes. Fifteen years later, yup, they've started to crack, but they're still rideable, though I don't think I'd do a blazing descent on them. 28's, radial on the off side and the front. My point -- much depends on the builder, and the rider.
Bloody tuppence worth,
Peter ("trying to do this properly") Bridge DenCO