It's been a while since I've updated this, but figured I would update it with what I've learned so far.
The speed is absolutely amazing. Most filaments now print at 250-300mm/s with a direct drive titan aero. I think there is more speed to be milked, but I'll need to do to a dual drive extruder and the apocalypse is slowing E3d down.
It has only skipped steps twice in the entire year. Both times the acceleration was at 8,000. 6,000 she would shake a bit, even in her weight class. It can handle 3-4,000 fine, but with ghosting on every edge. Currently it is at 1,800. I'm currently using 6mm belts and the next printer will have 8-12mm. I would/will probably make the next one 1-200lbs/100kg heavier too.
Reliability. This is after all the main reason I built the thing. I went through the other day and started checking fasteners. Not a single one has come loose. Neither has any of the brackets, connectors, etc. I have found myself leaning on the bed while oiling a rails a few times, and when I check the level it's still perfect. I would say this category has been a success.
Temperature. I had always theorized that corexy would heatup the chamber above the build plate before the rest of the chamber. What I didn't suspect was that these 2 zones would never balance out. Above the build plate will always be 10-20 degrees warmer than below. This could also be a side effect of the electronics chamber sharing a common wall. That said, I have seen chamber temperatures of up to 58C with a build plate temp of 110. Most times however it bounces between 45-50. This is with polycarbonate side panels. I will eventually insulate the build chamber and get that up higher, though I have yet to see any prints crack.
Dialing in filaments. I've found most slicers dial in settings like retraction in 0.2mm increments by default. I have found that with many filaments I need to dial that in at 0.01mm increments. I had an ASA that would leave blobs with a negative restart distance of 0.04, and holes at 0.09.
Electronics. This is often the most neglected part of builds. First off, DIN rails. They are amazing. Mounting all my electronics to the side panel makes them wonderful to work on, add things, troubleshoot, etc. Since it is cooled by fans and sharing a wall with the printer however, it is pulling heat away from the build chamber. I will eventually move them to a drawer at the bottom of the printer.
The biggest thing I learned is it is going to take longer than you think. There is a lot of information out there for what I would classify as hobbyist grade printers. While a lot of that wisdom will carry over, a lot of it won't and you need to figure out what does or doesn't. You often pay more for this when you buy a machine, than the machine it's self.