When doing MRs, I balance time and financial cost, so I like the more-miles/fewer-days approach. One way to get there would be:

Same-day SEA-PDX-BOS-SEA - 5520 EQMs for $373 r/t
Same day SEA-MSY-SEA - 4160 EQMs for $336 r/t

That's about 7.3 cents per EQM, which isn't all that great, but better than some (and it's only two days, as opposed to three).