Whats diferrence between video card?

[hobbax]

I have an ATI RADEON HD5450 1GB DDR3 CEDAR but now it will burn so im most likely changing to AMD RADEON HD6450 1GB DDR3 SAPPHIRE whats difference? Clock for HD5450 is GPU CLOCK 650MHZ , MEMORY CLOCK 533MHZ im not interesting in upgrading for gaming but its the cheap that i see, i've readed page but still no find difference

I've find that different companies that makes card have lower clock than others