You can't really use a "silver box" adapter for game playing. Most games don't support DoublePAL, VGAOnly or rarely DoubleNTSC screenmodes. The ones that do are very slow in these screenmodes because the display DMA has to read each row of pixles twice per display.
If you want to play games on a VGA monitor, you need a better adapter with a scan-doubler built-in. This will allow you to run games in standard PAL mode or NTSC in a few rare cases.
