You need to get some bits designed for wood. Up spiral and down spiral. The down spirals work great to prevent chipping on the top. If you want the best of both worlds try a compression spiral. In the meantime change your calculations a bit. Feed in ipm is rpm x chipload x number of flutes. I can't really say if the .01 chipload is best but it's not a bad start for a 2 flute 1/4" tool. Try half that for 1/8 to start with the same 1/2 diameter step down. Using the formula you would get 540ipm for the 1/4 and 180 for the 1/8 at your same rpm. Doesn't really sound realistic for the 1/4. Try reducing your speed to 8000 and using a .007 chipload. That would be 224 ipm. Again the four flute will probably be problems no matter what you do but worth a try. Good luck.
Ben