I was looking through a website for parts to put in by PC that I am working on, and I came across a HD 7870 with a 1100 MHz and a HD 7950 at 800 MHz.
My question is does this mean the 7870 will be faster then the 7950?
The reference 7950 would still be slightly faster due to more memory bandwidth and a higher shader count. Keep in mind that most 7950s these days ship with the boost BIOS that moves the stock clock speed up to 900MHz, which would give the 7950 a much bigger edge.
The 7950 would also have much more overclocking headroom compared to the 7870, which depending on the model will likely top out somewhere between 1300 to 1400 MHz if you are lucky. The 7950 are often hitting 1000MHz, which combined with the higher shader count and higher memory bandwidth means much better performance than an overclocked 7870.