The 5AX is my personal favorite SS7 board. I have two of them and will never sell/trade them. Both rev 5.2. one is my goto DOS rig, and the other is for specialty games and demoscene stuff. For DOS, I simply can not think of a better motherboard.
I have a few Asus P5A's, but I find them to be more "fidgety". I don't think they handle PnP very well. It's always a big struggle getting things like the AWE-32, Gravis Ultrasound PnP, or ProAudio Spectrum 16 going on the P5A. Oddly enough, my SB-16 (CT2230) has no issues on install. But every other PnP or sudo PnP card (as in software setup and no jumpers/dip switches), just never installs correctly. I always have to edit or change some file or line in something.
I never have those issues with the 5AX. It's very well behaved. Hell I'd feed it treats and pet it, if I thought it wanted that,