Personally, I went for the 4600+. Same clock speed as the 4800+
For me, price was a bit of an issue and everything I read indicated that the 2x1MB L2 cache in the 4800+ over 2x512MB in the 4600+ basically amounted to nothing. It certainly didn't make the price difference worth it.
For multi-processor aware renderings that I do, it benchmarks (specific to my application) exactly the same as the 4800+. The extra cache size made no difference.