You need to list your SP's. Might be a good idea to try and sell someone high, but can't suggest without info. I know that guessing when a pitcher will do well or when he won't (aside from starts in Colorado) is dicey and often frustrating when it backfires.
I would do a couple things....drop your worst starter...and also play the matchups like you said. I would just consistently reduce the number of innings rather than just bench everyone and take a big drop in the standings.
I would snatch up some of those undervalued middle relievers. They DO help with your %s, Ks, and Ws.
plus many more -
Middle relievers are one of the most underused commodities in FBB, but they are quite effective. In roto, because of the IP limit, one way to look at pitchers - all pitchers - is what they do per IP, and many of these middle relievers stats per IP blow away most SPs.
First...don't do anything drastic. You aren't so far over that you need to worry. In that format the ideal set-up is 5 starters and 4 closers. Starters 1,2 and 3 start almost all the time. 4 and 5 start about half the time, in favorable circumstances.
In the spot you're in, I'd follow the above procedure, but I would put number 3 in the "part-time" deal with 4 and 5. until the projected overage comes down to about 10 or less.
I agree with Slomo. Drop your weakest starter and go with just four. If a good middle relief pitcher, i.e. Lidge, is available you can grab him. But I think with 4 starters you can get the innings pitched overage down. But I wouldn't wait too long to do it.
Never bench the top guys (RJ, Prior, Schmidt, Schilling, Pedro, etc.) just because you felt like starting Sergio Metre a month and a half ago, for example; it means you're giving starts to mediocre pitchers instead of the top ones on your team. What I suggest you do is figure out how many pitchers you were supposed to start to stay under the max, and then pitch one less. For example, in my league, a 4-man rotation + 3 closers will keep me around 0 or even in the minuses. So, I'd drop or trade my worst starter (or just bench him) and go to a 3-man rotation until the innings go down. Don't sit your good pitchers just because you felt like spot starting some joe schmoe a month ago...
An unanswered question is better than an unquestioned answer