Apparently, there has been another BETA floating around ASUS's Technical Support (0601) since last month.
I have flashed it few days ago, but unfortunately, symptoms are exactly the same as with 0503 - look few posts above for explanation. I was told, that ASUS is aware of the problem with HDD's off/on before loading OS and are trying to fix it. But definetely, 0503 and 0601 do not have a problem with restarting, when overclocked, at least for me. That's one step in a right direction, right? :)
Anyway, I decided to add both BETA's to my host - feel free to play with them ;)
0503 BETA ---
0601 BETA
:peace: