That's fine, but note that if you define -mcpu=arm1136jf-s, qemu (used by scratchbox to emulate an ARM processor) won't be able to run the resulting binary (this may cause problems if intermediate binaries are used).

Personally I just use "-mfpu=vfp -mfloat-abi=softfp"

X86 target allows you to startup the maemo gui and see what an app will look like. I never use it, I perfer to test on the device.