I had a close look at your code today, just trying to see the difference between VGA and composite (PAL)
I believe the VGA line is 32us, whereas the composite line is 64us, so basically it is much harder to squeeze pixels into a VGA signal !
I have just written a new PAL driver for ATMega1284, its 352*280px, it reads BMPs off an SDcard and displays on the TV.. I still havent implemented that jitter fixer.. I havent got my head round it yet !!
I am using timer1 running flat out at 24MHz, I really wanted 32MHz but the '1284 couldnt handle it !! ha ha
Be really good to get the screen flicker free
ANYWAY.. your project looks awesome, I must try it when I get a chance !!