Unless I have missed it, no one here has posted the difference between the 3800+ X2 and the 3600+ X2. The 3600+ is a 65nm process, while the 3800+ was manufactured using the older 90nm process. I'd definitely go with the 3600+ X2 if I could. Just my $0.02.
Considering the problems 65 nm has at both clocking / memory dividing due to odd multpliers / latency this is a bad recommendation.
A 65 nm 3800+ process for example, will on average perform about 100 model numbers down, a 4800+ 65 nm processor, for example is yielding on average the same rough performance as a 4600+ 90 nm processor.
The better deal for OCing and all around performance is the 3800+ 90 nm... avoid 65 nm for another 2 quarters if you can.
Also, AMD does indeed make a 90 nm 3600+ which will likley nudge out the 3600+ 65 nm processor in terms of performance.
There are a handful of reviews out on the 65 nm process not meeting expectations:
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2889
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2893
http://firingsquad.com/hardware/amd_athlon_64_4800_65-nm_preview/
http://www.trustedreviews.com/cpu-memory/review/2007/01/18/AMD-Athlon-64-X2-5000-EE-65nm-/p1
(woohoo 3.0 GHz limit on a 5000+, less than 90 nm....

)
Techreport and Lost Circuits have also done reviews...
Jack
I don't know about the 90nm 3600 outperforming the 65nm version. The 65nm version has double the cache and 100 fewer Mhz. Head to head benchmarks would probably be needed to get a good idea of how that affects it. I'm also not sure how overclocking is for both of them, but 90nm is pretty proven and it seems that the 65nm versions might just be the lowest performing 65nm Brisbane chips being sold off, so they may not do well at all.