With all due respect, you shouldn't even think about comparing BOS vs. BDL. Granted DFW is always tough for upgrades, but you'll have a much better success rate flying to smaller, lower-demand airports (e.g. BDL) as opposed to one of the toughest elite-upgrade routes (e.g. BOS-DFW, AUS-DFW, LGA-DFW, etc.). The upgrade will likely still be tough as you're still down a bit on the totem pole but I can't comment on that specific route given I've never flow in or out of BDL.