What effect will sharpening a symmetrical wing's leading edge have on performance? I guess I can assume it will have less drag but what about low speed performance, stall, aerobatics, etc? I'm not talking a drastic change...just a slightly sharper leading edge. I'm building a Sig King Kobra and have some pre-shaped leading edge stock that I'd like to use instead of carving my own. Any thoughts?

For speed there won't be much difference. But a sharper LE is supposed to produce an earlier stall all else being equal. In your case it may be complicated because if you're using a sharper LE shape the area just behind the front radius may be changed enough to produce issues.

But it should snap roll easier.

Biggest change, a sharper more sudden stall which is usefull for entering snap rolls or spins.

In actual practice -I have never seen this to be effective.--on models
a blunt LE -if the model is pitched quickly works every bit as well.
IF the airfoil si simply thinner then it works best .
- The flat board 1/4" thick wings used on outdoor foam models will snap blindingly fast - with only slight pitch and yaw .
The sharp LE snap theory belongs with the thick wing producing more lift theory
No basis in fact.

I HAVE BUILT 4 COBRAS.. THEY ARE FAST AS IS.. OS .61SF,,11.7 PROP,PIPE .. REAL FAST!! I THINK THE STOCK WING WORKS SUPER,,LANDS VERY SLOW.. RETRACTS ,,THIN TRAILING EDGES,TIGHT WING TO FUSE JOINT,,,WILL HELP MORE THAN LEADING EDGE SHAPE.. HAVE FUN--------- RD

Dick Hanson is correct in that at the Reynolds numbers at which we operate, and with the tremendous power to weight available to R/C models, any difference is too small to notice. On the other hand, if the intent is to understand some of the finer points of airfoil design, BMatthews and Rodney are also correct. All else being equal, a little sharper radius will usually cause a slightly more abrupt stall.