What you say makes sense, however the benchmarks used standard sw, which should be mostly single-threaded, e.g. see: http://www.amd.com/us-en/asset...ance_Comp_Q2-2006.pdf.
Both single core and double core processors are compared and we have a +125% for a 3800+ and a +134% for an X2 3800+, thus the benchmarks took little advantage from the availability of two cores and should account mostly for the brute force of each core.
For these reasons I was expecting more computational power from each core. As we know, this is not determined only by clock frequency, but also by architectural design of the processor, which I thought it was improved from the 3000+ design, but which is perhaps the same instead, this thus explains my results, as you said, but at this point is not clear to me how AMD could report a +163.5% performance for an X2 5000+, which implies an estimated +170% performance for an X2 5200+.