I have two 8.5' solid Birdviews and my experience on C-band is different from Titanium's. The Birdview factory scalar does not end up mounting at the right distance, at least when used with modern feeds, for both orthos and servos. You will get an improvement by removing the hexapod legs and fashioning your own feed legs, which will allow you to use a better matched scalar at the correct focal point and set to the appropriate f/d.
I don't have a DP-4, but I own and have tested other dual orthos, and know someone who is very happy with their DP-4. While corotors are ok, they perform worse than any single or dual ortho feed. I have carefully measured this on every C-band dish I own, and I currently have eight set up, and two others I used in the past. The single orthos (C-band only) are pretty much the gold standard. A dual ortho on C-band is about 0.5 dB worse in CNR than a single ortho, while a corotor is generally more than 1 dB worse. Dual orthos aren't incredible on Ku-band, but as the Birdviews are high f/d dishes, dual orthos work better on them than almost any other prime-focus FTA-level dish. With all the gain of a Birdview, Ku reception is never a problem with a dual ortho, and better than a corotor by a country mile. Also according to my friend, the DP-4 is a better performer on Ku than the Chaparral and ADL dual orthos. In terms of skew adjustment, satellite operators keep their bird polarizations dead on. Once you have an ortho aligned, there is nothing that tweaking skew is going to help.