I can tell you that ZFS is pretty stable and just as fast on Linux because I tried it recently. I still prefer ZFS on Illumos (Open Solaris Fork) or Oracle Solaris because it is proven mature, Solaris isn't messy like Linux for storage/network operations, and because Solaris has an incredible debugging tool called DTrace that will analyze anything on the server.
I checked those comparisons, but I wouldn't take that Postgres test to the heart because;
2x Xeon 5450 (V0 (code name Nehalem), old obsolete 1,333MHz Bus, Dual Channel DDR2 most likely as ECC/Registered (adds some latency), 3GHz 4-core (no HT), 12MB L2 cache)
1x i5-2500k (V1 (code name Sandy Bridge), QPI 5GT, Dual Channel DDR3, 3.3GHz 4-core (8 virtual), 6MB L2 cache)
I am actually thinking of playing around with Postgres and its settings on Solaris. To be honest I never used it, but I am intrigued to test my machines, and also test it under Linux to see if I also hit a problem. You can always install Solaris on the Dell server and see if you also have performance issues there with your settings. The Solaris OS is very easy to manage and I'd be glad to set it up quickly with you.
As for the Dell Perc controllers, I doubt there is an actual performance difference other than available RAM on the card to push for more write-back buffer capacity. It uses the exact same CPU and such. Either card will be just as incredibly fast.