Did you try the manual in case there is something useful?
I had a look now and must admit I don't understand most of it, among others the meaning of some of those acronyms.
The setting I have now is surely not satisfactory to run VL59 with vega set to 794 and that fbdev driver. The problem is naturally not confined to megamario, etc. It is with all programs requiring full screen to run. A way around is to stay with savage driver and leave X for full screen programs to run.