gcarter, petrel doesn't use an OLED screen, but I haven't had any issues with it, though most of my diving is in a cave, so pretty much everything is bright enough. That said, I haven't had any issues with it in bright OW though minimal.
To the OP, there is a reason the information is as sparce as it is, regarding the Q, it should also say something that Dive Rite is using the Petrel as the controller and backup computer for their rebreather instead of modifying the Q. The Q isn't a bad computer, but for less than $200 more you can get a badass computer that will hold value better and work better for you. Regarding the xdeep, there is a lot of issues that have been reported, but not sure of recent issues. For the features and price, I think the extra $100 ish for the Petrel is a nobrainer. If you were looking at a different price bracket, say the $400 range, then it is a different discussion, but when you're debating $650 vs $750, it's not even a discussion at that point.