My question is, does 5x1 portrait setup add any FOV above a 3x1 portrait setup?
Yes it does, there must be something wrong with Dirt3. Most likely it's detecting your eyefinity setup through AMD's APIs and going off that for FOV adjustments.
If Dirt 3 is like Dirt 2, you should be able to change FOV settings. I believe it was Automatic or something like that, that I got to work.
If not check to see if there's a console where you can manually adjust the FOV value.
Is the FOV stretching because I am using SoftTH?
It might be SoftTH. What I would do is, go into windowed mode, then move and expand the window so it fills all the screen.
If I were using all HP LP2065 monitors and a Eyefinity 6 card would I still be getting the same result?
You would get the correct result, because Dirt 3 should be able to detect your eyefinity settings.
One other thing you may want to try is, un-grouping all the monitors, the using SoftTH to setup the resolution, so Dirt3 doesn't detect eyefinity is in use, then it should give the correct FOV.
This may increase overhead though.