Stability is my number one priority; running hot in and of itself isn't a concern for me so long as it's within its specified operating temperatures, but if it leads to the card shutting down more often than not as stated by one reviewer under "normal" usage and conditions, then it's off my list.
After stability, it's then price, and finally performance.
Is the Intel X520-DA2 an SFP+ card? I've been searching but can't seem to find a 10GBase-T version. SFP+ adds additional expense due to the transceiver modules and cables or adapters. What's also of concern is your experience having to switch to Cat7 to realize full speed. My whole house network is Cat5e that I pulled myself. Now, I could replace the lines going to rooms that will service 10GBe clients, but would prefer not to have to do that (I've since overlaid a plywood subfloor in the attic to facilitate storage so it would be a lot of work to move junk out of the way and unscrew the subfloors off to get access to the long wire runs).
Which then leads me to debating if the AQC107's are speed sensitive to the cables; if they are already inherently slower than the Intel's, but aren't sensitive to Cat5e vs Cat6 vs Cat7 wiring, it may very well be the best overall option for me. I just want to avoid any reliability issues as suggested by an iMac Pro user I posted about earlier...
