i bought a sapphire 4890 in the summer and i just overclocked it for the first time using ati overdrive auto tune. when i played crysis warhead with the overclock settings there was so many artifacts so i exited the game and turned off overdrive and put the stock clocks back on but now when i play crysis theres still artifacts and they wont go away. and they dont happen right away either, they start after about 10-15min of gameplay. will saphire warranty my card? nd should i tell them i overclocked it or leave that part out?