Which QB in a salary cap league?

I'm in a salary cap league and there is a flex position that can be any category (QB, RB, WR, TE, K, or D). I currently have Brady as my QB and have Romo as my flex starter. I want to stay with a QB in the flex position, because they are the hot, reliable fantasy players this year.

But, I'm concerned about Romo's matchup against New England next week and wonder if there is a better option out there at QB.

To stay under the salary cap, the only QBs I CAN'T afford are P. Manning and Brees. Otherwise, I can pick up any other QB in the league for this position. Here's who I'm looking at:

- McNabb (PHI @ NYJ) - NYJ is 25th in pass yards allowed

- Rivers (SD v OAK) - Rivers shredded DEN and has #22 OAK passing D at home

- Culpepper (OAK @ SD) - #27 SD passing D gave up 232 passing yards, but 0 TDs, to DEN last week

Should I stay with Romo, or pick up someone else this week? Maybe in another position other than QB (I already have LT)?