ROPS/LOPS isn't the whole deal - especially for relievers.

It doesn't take into account walks (and probably not HR/IP).

Example: Andy Pratt has LOPS/ROPS of:
.500/.667

But he gave up 7 walks in 1.2 IP. Don't use him with the bags jammed and a tie game.

Also if you have one guy with much better OPS vs RH or LH and the other guy even ROPS/LOPS, it would depend if you are facing a team with all RH or all LH batters, an even mix, or a few really good RH batters but only mediocre LH etc.

My main point though is that you can't just look at OPS. Walks/IP, K/IP, HR/IP, GB/FB and probably even SB/CS pct are important.

[As I'm sure you know.]