OK. Makes sense. Since you have a Sandy Bridge processor, I recommend a Sandy Bridge Gigabyte motherboard. (You can use the 2600K on an Ivy Bridge 7-series motherboard, but it's a PITA to get running.) I have three Gigabyte Z68 motherboards, one of which is the
Z68MX-UD2H mATX in my Mac Pro case mod. Like my other Z68X-UD3H ATX size motherboards, it takes to OS X w/o a huge effort. Matter of fact, there is a very useable DSDT in the tonymacx86 DSDT Database which I still use although I'm running Mavericks on the Mac Pro case mod system. However, I've tested the installation Yosemite 10.10.1 on my Son-of-Zorro system (Z68X-UD3H / i7-2700K / ATI/AMD HD 6850) and 10.10.1 installation went very smoothly. So, you shouldn't have a problem with the Gigabyte Z68MX mATX motherboard in a G4.
I, too, have a Mac G4 Sawtooth that I've been waiting to hack. I also have a
Gigabyte H67MA-USB3 mATX motherboard running an i3-2125 processor which is also an easy OS X candidate for you using the appropriate DSDT fromt he DSDT Database. I've got the
Laser Hive G4 mod kit and am just waiting for sometime to do this mod and put one of the Z68X's in an old G5 that I also have hanging around.
So, not wishing to hijack raphyv23's thread, those are my recommendations. Disclaimer: I have not tried to hack any other motherboard manufacturer's products - just Gigabyte's.