I've been running 10Ga wire. I can't be sure but it seems to make the system slightly faster, although it could be expectation bias.
I will definitely try a bigger gauge - I have been running 18awg.
I replaced the PS cables to the Supravox widebanders (running 170hz to 5khz with 1st order filters) today. They were actually 22awg, and I made up some 8awg cables from Cat5. You were right, there was a noticeable in attack, speed and presence. I did one channel at a time, and there was an obvious difference.
The PS cables on my bass drivers are about 12awg, so I will try making them bigger next.