Right, you want something which is a multiple of what you want to display... problem is only producivity mode (native) falls into this category at 640x480. Everything else (scan doubled ntsc/pal) looks like crap.
I found that productivity mode looked excellent on my LCD monitor, but double ntsc did not... and it still flickered even with the scan doubler (worse actually).
I sold the scan doubler and bought a 1084s monitor.
However, I just picked up another scan doubler.. I wanted to try it with a CRT this time and see what I thought.