Hey man, to totally solve the youtube hd lag problem, go to cwm recovery and format sdcard.
I saw that solution long time ago and I didn't try. ( that solution was given by a samsung customer service). I tried several days ago and , wooow, it works.
But remember, it works on ICS only. Neither 4.3 or 4.4.
So, my recommendation is not to flash any 4.3 or 4.4 rom. toldo's ICS roms ( stock or jellybean ics) are the best choice out there. If youtube HD is not essential to you and you really want to try newer verisons , I would suggest OMNI 4.3 rom , not the 4.4. The Omni 4.3 rom is the smoothest 4.3 rom. of course, the youtube hd is still lagging. even you overclock it.