Hi TJCOMBO,
The modelines for Galaga and MK2 are correct, so you've got everything right.
- Galaga runs slow because we can't make a 15-KHz modeline with 288 lines that works at 60 Hz, we only can get 51 Hz or so, so when vsyncing the game's speed is reduced accordingly. If you wan't to run Galaga at 100% speed create an specific ini for it and add the option -triplebuffer. Bear in mind that you won't have smooth scrolling as the refresh will still be 51 Hz.
- MK2 modeline is right but you only get 98% speed, that's very probably a CPU issue, I'm afraid.
As for the fact that these resolutions don't fit the screen, you probably need to get more accurate monitor_specs. If other resolutions are fine, then you need to define a subrange for the odd ones were the right margins are defined. There are several threads in the forum were this is explained. You need to use Arcade_OSD, tweak some modelines and use the values obtained to create new monitor_specs from them. Not too difficult if you know what to do, but it requires some patience. However, not many users go that far, but at least the tools are there for any one.