well, it's taken a while, but I have slackware64-13.0 on a test machine, and apart from problems with nvidia drivers (i descovered you need to let the installer install the 32bit opengl drivers (even though I have not installed any 32bit compatability libruaries) to get xwindows to run at anything above 640x480.) I now have it working. Allowing for the differences in processor speed on the new test machine, there still appears to be a 15% or so improvement in speed running slackware64-13.0 on qwmu 64bit on a slackware64-13.0 host
I also don't have to use any kernel compatibility qemu options to get the virtual machine to start. It is still many factors slower than native, so I'll look at the kqemu or kvm options and report back. I have also yet to try 32bit slack as a guest on the new 64bit host.