Which presets should I use for my PC monitor?

[Stremon]

I recently installed groovymame to use with my PC CRT, but I wonder which profile I should choose between 30khz or 70khz.
Or maybe a custom present?
I got a Iiyama HM705UC, that accept any signal from 640x480@60~170Hz to 1600x1200@60Hz.
I tried both 30khz and 70khz, 70 seems like it unlocks more resolutions, but groovymame only wants to display 640x480 with it, no matter the game resolution.
What mode is recommended for my display?
If better to do a custom preset, how can I find the data needed for my monitor?
Thanks 

[Calamity]

I tried both 30khz and 70khz, 70 seems like it unlocks more resolutions, but groovymame only wants to display 640x480 with it, no matter the game resolution.

Post a log, it's possible that it's just defaulting to 640x480 due to a configuration problem.

Existing presets are a bit restricted to benefit from your higher resolution. It's easy to create a custom preset, on the other hand.

You need to decide whether you prefer it to be able to switch resolutions (e.g. 480p to upscale 240p), or to use fixed higher resolution, like you'd do with an LCD, and just adjust refresh rate. If you prefer the later, you can use this guide directly: http://geedorah.com/eiusdemmodi/forum/viewtopic.php?id=374

[Stremon]

I tried both 30khz and 70khz, 70 seems like it unlocks more resolutions, but groovymame only wants to display 640x480 with it, no matter the game resolution.

Post a log, it's possible that it's just defaulting to 640x480 due to a configuration problem.

Existing presets are a bit restricted to benefit from your higher resolution. It's easy to create a custom preset, on the other hand.

You need to decide whether you prefer it to be able to switch resolutions (e.g. 480p to upscale 240p), or to use fixed higher resolution, like you'd do with an LCD, and just adjust refresh rate. If you prefer the later, you can use this guide directly: http://geedorah.com/eiusdemmodi/forum/viewtopic.php?id=374

What the best way to create a custom preset?
I saw in other post I have to create a log with GM, but the -log option doesn't give me anything except the errors I might have, so I might be missing something.

Ideally I would like any game to be displayed in their native resolution, only with 120Hz for resolutions < 30kHz.

Right now it's working perfectly with the generic 30khz PC CRT profile, except vertical resolutions higher than 512 are not added to generated modes.
They are however generated on the 70kHz mode, but this mode doesn't support resolutions lower than 30kHz.

So I guess the best solution is to create a custom preset for my monitor
On a side note, are there a lot of mame games that use higher vertical resolutions than 512? I guess rotated tate games do?