Don't run them lean, I can tell you that much
I've done a bit over 400hrs in a SR22 and I'd say that 98% of the time (spent in the cruize), the engine has been run at 60° to 70° LOP. The engine runs cool, it runs smoothly and it runs nice and clean. No cracked cylinders, all the compressions still in the low 70's and a qrt of oil once every 25 hrs.
The IO-550 as set up in the SR-22 is one smooth running engine (better than the IO-520 in the 210 I have to admit), whether it's run ROP or LOP.
Depending on the actual power setting being used (when running it LOP), you'll save up to 5 usg/hr for a loss of around 7 to 9 ktas. Can't vouch for the SR20.