How safe is it?

Right, here's the brief.
My ATi HD5670 Sapphire 512mb Runs 775mhz stock clock, and 1000mhz stock memory.
Ive put the clock up to 825mhz, and the memory up to 1100mhz. The stock fan speed is 60%, But ive put it up to 80%.
Tell me, how safe is it, and how much of a differnce will i see?

Thanks.
P.s. if you wanted to know, my system is....
AMD Athlon X2 215 (Swapping to a Phenom 965 soon!)
Ocz stealthxstream 400w psu
4gb DDR3 1066mhz Ram
1x 92mm led fan