yep, you're right
from my tests with a lot of athlons/durons it can confirm that.
i encountered those "fsb walls" on older athlon/duron cpus with t-bird, morgan, spitfire-cores.
but the athlon xps already have almost no problem with 200+
i've looked a bit through the 8600s categories. those results there were all done with gddr3 equipped cards. so the right category would be that one
http://www.hwbot.org/hardware/videocard/geforce_8600_gt_ddr2
but his card only has half of the shaders as the others, so there should be a new category made.
http://www.hwbot.org/hardware/videocard/geforce_8600_gt_ddr2_16_shaders
i renamed the others with "gddr3" so its clearer to see under which category to submit.