The 9800 is from a completely different generation of hardware, the "specs" are simply not comparable. It's akin to wondering why a 3.8Ghz Pentium 4 would be slower than a 1.6Ghz Core i3 CPU. The newer architecture is more efficient, has newer methods and technologies, etc.
If I were buying a new GPU right now I'd be looking at a GT 970. Sure it's a lot more expensive, relatively speaking, but it's going to be soooo much faster.
- Oshyan