I'd buy AMD

Generally speaking, Q9450 is faster than 9500, but the gap is not that huge. Q9450 is not a native quad design. It has 2 dual-cores inside. If you take a close look at the cache of the Intel CPU, you will see it has 12M L2 cache, but pay attention to 2x6M. On the other hand, AMD phenom 9500 has a true quad design and its cache structure is 4x64K L1, 4x512K L2 and 2M L3. Giving the fact that L1 cache is much faster than L2 and Intel dual cores need to sync to access the L2 cache. Although Q9450 has 12M L2 and 9500 only has 2M, the difference is not that huge. Clock-wise, Q9450 is 2.4GHz while 9500 is 2.2GHz. Benchmark tests have shown that Q9450 beats 9500 overall but not as the cache and price suggest.

So, considering what you will get from $1,550 vs $820, I would buy an AMD for a desktop PC or a home office server.