mSATA as a boot disk?

I have an R2 and was thinking of replacing the wifi module I don't use with a mSATA hard drive. I would want to boot from this drive. I have read that there are some R2 motherboard that don't accept over a 256GB drive. Anyone have this issue? So when setting up the mSATA, in the BIOS am I going to be able to set it as a boot drive that would be a priority over the existing hard drive. I want to use the 1TB drive as storage but want to make sure that Windows won't try to boot from that drive first. I have read that sometime the BIOS does not have an option to set the mSATA as the priority.