Yeah, it would help knowing the horiz/vert refresh rates. Keep searching, if you happen to stumble across a manual, or find those values some other way. The config file should not get overwritten by anyone except for you yourself, or if you run some configuration program that writes to the file. Running X itself shouldn't modify the file; are you sure the changes you made were saved in the first place? The file needs to be edited as root, so make sure you are doing it as root.
or use any other editor instead of pico.
Try also commenting out the DPMS option:
Identifier "Generic Monitor"
It might or might not help, it did allow me to get some resolutions work some time ago when they didn't work all right. If it doesn't work/make any difference, uncomment the line again, just in case.
A backup of xorg.conf (the working one) is all right; if/when you happen to mess up the configuration so badly you can't get it fixed, you can simply copy the backup over the non-working config file and it should work again.
You could also search the web for some "general" horiz/vert refresh rates for a monitor that resembles yours. The values are pretty important to be right if you set them, but I'm fairly confident you could try some general values to test with. Probably, if they're not right, they just throw you an error and that's it (I don't think you can get the monitor explode, but if you do, I'll now say I don't take any resposibility about that