Loop order doesn't matter, so the rads before, in between or after the any component won't make a difference in temps.
Like saint19 mentioned, you'll likely need something along those lines, considering you are assuming a 'normal' thickness rad like a XSPC RS series, not a thick one like an XSPC RX series or TC PA. In the sense that you would use a normal rad, a 2x120 rad per CPU or GPU is a good rule of thumb.
Do you want this moved to the watercooling forum?
Wait...nevermind...it already is here. For some reason, I thought I was lost in air cooling. My fault.