I've been in a league that has used obp for years. We all love the cat. as it makes people who are valuable in real life valuable in roto.
A good pitching cat. to add is holds if you want to use MR's.
My league uses a 6x5(1.2). Which means that we use Avg,OBP,hr,rbi,runs,sb's and then multiply the pitching cat. by 1.2. This work amazingly well.
Also if using OBP be sure to look at guys like Drew and Mora.
An unemployed jester is nobody's fool.