My one piece of advice on choosing a sscx frame, is deciding what chain tensioning method is going to work for you. I had an ebb for a while, but having changed to adjustable dropouts, it makes changing gear so much easier.
I'd get something with rear facing dropouts ideally. Or if a total bargs comes up on a well know auction website then an eccentric rear hub or BB (depending on BB type). My immediate thoughts were a pompino but they seldom have XL in stock.
My one piece of advice on choosing a sscx frame, is deciding what chain tensioning method is going to work for you. I had an ebb for a while, but having changed to adjustable dropouts, it makes changing gear so much easier.