The warranty covers all overclocking so there is no need to worry about voiding the warranty unless you fry the Card. Just make you that you use these 2 programs to test for Stability & no artifacts after your down testing
GDDR5 memory also does not artifact, it reduces performance after reaching the magic number. Increase memory speed in small amounts till performance starts decreasing, then lower it to get back to the magic number.
Happy day. I have a HD 4860 that I've owned for 11 months, and I never overclocked because it was limited to 710/760 with the stock BIOS. I never knew you could disable the maximum OC limit with that cheat, and I never risked flashing the BIOS. Thank you so much.