Cartman was being a fat bastard, so brad and I kicked it around a bit.
Things were slowing, and brad had recently started shuffling tables across the two pairs of drives inside cartman... but it wasn't enough. Tonight, I grabed the wonderful sysstat set of tools for linux and started running iostat, while watching mytop.pl in another window. Directing Brad as to which drive is getting the most reads/writes/s.
So, we finally landed on a good balance. SDA is getting slightly less reads, but slightly more writes, and SDB is getting slightly more reads, and slightly less writes :)
Now, all of a sudden, I CAN GET TO MY FRIENDS PAGE AGAIN!
Celebrate! Just not so hard, cartman's still not doing so well ;)