To find out what stairs you can currently challenge someone in, first go to the Main Stairs Page, then click on "Show your stairs only" link. The ones in BOLD are ones you can make a challenge in. .
My sympathies to the topplayers (top dice rollers in backgammon) who must play lower rated players. If they should lose (awful thought!!) they could lose some of their so well deserved BKR. If i was a top dice roller i should absolutely restrict myself to not playing any stairs at all