ORIGINAL: blw
Look at the replacement prices of sleeves and pistons between Evolution and OS, and that may make up your mind for you. In case you crash the engine some day, compare prices of the crankshaft and case.
The reviews by Clarence Lee pretty much validates the same quality between both brands in the other sizes. I would give Evolution the edge for using chromed liners, and the 3 year warranty.
Good points! I just replaced a piston and sleeve in an Evo 1.00 NX for $40 and the replacement P&S for an OS .55ax is $89 and would cost $112 for my OS .91fx[:'(]