When to middle?

[iillllii]

A couple times recently I've had a chance to take a middle position, but am not sure when it is profitable. At lines of -110 on both sides of a bet, is capturing one number worth paying the vig on any other outcome? How many, or which, numbers do you need to capture to make it profitable?

Examples:

-A few weeks ago, I had $110 on Texas A&M -6 vs. Oklahoma St to win $100, and by the time the game kicked off, the line was Texas A&M -7.5. By taking Oklahoma state +7.5 at $110, I win $200 if A&M wins by 7, I win $100 if A&M wins by 6, and I lose $10 on any other outcome. Since I have a key number here (7), and 6 is good too, I suspect I should jump on OSU +7.5 every time here?

If that is an obvious place to take the shot, where is the threshold? If the line had merely moved to OSU +7, I win $100 if A&M wins by 6 or 7, is this worth the $10 hit on any other outcome?

-This past weekend, I had $110 on Toledo (pick) vs. Ohio, and by kickoff, Toledo was a 1.5 favorite. I could take Ohio +1.5 to win $200 if Toledo wins by 1 point, but I'd lose the $10 vig on any other outcome. Doesn't seem worth it here....

-This upcoming weekend, I have Oregon -2.5. If the line moves to 3.5, do I jump on USC and hope for that 3 point Oregon win?