A quick update. Rapture is definitely not stable under Win 7 x64 - it took Reaper out the water after just a minute or so of browsing around patches.
(I think I was using the 32 bit version of Reaper at the time). Dim Pro seems fine, though.
That probably explains the crash I had loading Dark European Space Adventures, so it was unfair to blame that on Sonar. (although Rapture is their product, I guess).
Someone pointed out here that Win 7 wasn't released when Sonar 8.3 was done. This is certainly true but Vista was out already. Although modern history has been rewritten so that Vista was some kind of weird bloated abomination that Win 7 magically fixed, the actual truth is that the OS kernel is very similar between the two and much of the negative press Vista attracted was due to it being run on machines that weren't, in actual fact 'Vista-capable'. There's an interesting story about how that came to be, but I digress...
In penance for being a little hot-headed, I will DL and check out Sonar X1 (since there appears to be no X2 trial version).
Also, for any people out there running the BCR2000 plugin I made a while back, now I finally have a 64 bit OS, I'm adding a 64 bit version to the downloads as soon as I can figure out why it isn't saving the MIDI port settings when I add it to Sonar. (I know I could have compiled one earlier but I never had any way of testing it).