Ok, 800x600 should be enough if that's easier to get going.
My only concern is that previously the best 'balance' of getting most groovymame games to properly fit my screen without lots of v-height adjustment was to reduce my max progressive lines to 256 and max interlaced lines to 512 (I recall some cutoff was happening in higher interlace modes for this monitor, and the max progressive was lowered for vertical games like galaga.)
Changing the max interlaced lines to 600 would cause groovymame/switchres to make that many lines available for mame games to use, wouldn't it? I'm just curious, it seems like it would reverse the cutoff I was solving before.
Basically, whether or not the 800x600 is *actually* 15khz isn't that important to me, I'm turning off the monitor before switching and only using it for remote vnc utility. I believe under xp and the older crt_emudriver I still had a 31khz 800x600 that mame didn't touch. It would throw the monitor out of sync (as completely expected) but gave me more real estate to use when editing remotely. I was using the utility quickres to make that change fwiw, and changing back to 640x480i before turning the arcade monitor back on.
It would seem like what I desire would be an added 800x600 user mode that won't alter the resolutions groovymame would pick, if that makes sense. Maybe I need to 'add' it and somehow exclude groovymame from using it?
Thanks for the response Calamity! (and the truly awesome software)