If all you care about it performance, then put the swapfile on the Raid which has faster read/write for large chunks. Also, put a spit-load of memory in the system so it doesn't have to use the swapfile at all.
+1 for "All of my important data is backed up nightly on a file server." A Raid 0 setup is 4 times as vulnerable to failure as a single disk. (Well, actually, if the probability of failure of one drive in time T is PfT, then the probability of failure of at least one of four in time T is [ 1 - ((1 - PfT)^^4]), which is pretty close to four times PfT but ever so slightly less when PfT is small.)