Got my Solaris 10 1/06 DVD kit yesterday. So popped the x86 DVD into my W2100z (running Solaris 10 FCS) and let it get on with it.
Upgraded without a hitch. Everything looks good!
The boxed set includes quite a lot of stuff, so I also updated the freeware, and added the Studio 11 compilers. I'm leaving the Java Enterprise System for another time - I'm not going to risk playing with it on my main personal machine!
One interesting thing - I've got a decent monitor (a Sun 21 inch CRT) on this machine, and it had been running at 1280x1024. I hadn't really had time to investigate tweaking Xorg to get it to run at higher resolution. After upgrading, it came up on its own at 2048x1536. This was a little over the top, so I dropped it back to 1600x1200, which is the max recommended anyway, and runs at 85Hz rather than 75Hz, and makes the text a little more readable.
Everything still works, all I need now is a little more time to get back into development work.