Yeah, the LAX-SJO-LAX is definitely going to be good for the QF earners... but of course you'll only earn Biz-class credit even if on a AONEX (caribbean/mexico are considered Biz).. so not as good as DFW-ANC or SFO-BOS which earn first class SC's.

I'll have to run my script on the latest schedule to see the longest flights.. LAS-POS or POS-LAS was a good one until recently.