Raid0 Setup M.2. vs HD/SSD?

I've been designing a Sager 8650 for college (hard budget of $1500), and I like it. Through XoticPC I got it to 16GB RAM, IC Diamond, a 1TB 7200 RPM hard drive, and a 120GB SSD hard drive in Raid0 form (or so it says, for $1499). However, on Sager's site, after applying all of the other identical customizations/upgrades, it doesn't allow me to put anything but identical drives in Raid0. So I can either go for two 128GB SSD drives in Raid0 or a 1TB 7200 RPM hard drive and a 128GB m.2. SSD drive....

Raid0 Setup M.2. vs HD/SSD?