Hello curt...
If I were you I would definately snag Pittsburgh with the +4.5 points your local is giving out and then get the pats at -2.5 with one of the online books...in my humble opinion you would be foolish not to do it.
I personally did the same thing with the Eagle game, the line opened with Philly installed as -4.5 favorites, I expected the line to move upwards closer to game time so I went ahead and bought the Eagles down to -4 and waited.
Just this morning ( Sunday ) I grabbed the falcons +6...thus in my middle I have the Eagles -4 and the falcons +6, meaning of course that I need the game to end with Philly winning by 5 points to collect on both ends.
The odds are longer of me hitting my middle needing a "5" but the Eagles did in fact have two home wins this season that landed on the magical "5" as they defeated Baltimore 15-10 and defeated Dallas 12-7...so I took the chance.
In your case of having the pats -2.5 and Pittsburgh +4.5 you actually need the pats to win by either 3 or 4 points to collect on both sides...and the reality is that most games do in fact land on 3 or 4 than most other numbers, so I would say GO FOR IT!!
take care and good luck!
Deb