For games that run at 50Hz/50FPS like Ikaruga the current solution is to change the cable type in the settings to VGA. This will force the BIOS and game to run at 60Hz and you will get the full 60FPS.
This will not work on all games as not every game supports the VGA mode like the PAL Skies of Arcadia.
Another tip. I just tried Street Fighter III W Impact (a 240p game) which only showed half the image with the nullPVR but if you set the cable type to VGA the game displays properly so if you run a 240p game and it doesn't show properly, try to run it in VGA mode.
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Intel C2D E4500 @ 3.6GHz
Asus P5N-E SLI
Point of View 8800GT OC
4GB Corsair XMS2 PC2-6400C5 DDR2 SDRAM
Windows Vista x64 Ultimate SP1