I ordered Solaris 6 from Sun as a developer, it cost about £30UK all in. I got Solaris 7, Sparc and Intel versions, and it runs just fine on my x86 systems. I also run RedHat 6.0, with KDE. The box set of Redhat retails about £80UK over here. It doesn't work out of the box, it required some basic knowledge of Linux to get X running period, and as of today I don't have a working ppp daemon, and can't use the X font server. Solaris installed in less time and ran out the box.
Solaris is what we use at work, because we can run it on servers that Linux is not COMMERCIALLY viable on. This is because we use BIG Suns with a good support contract from Sun. This is not available with Linux yet, though I dare say it's not far off.
I agree Linux is faster, but it's also less stable. I had hardware problems installing RedHat where a duff SIMM caused it to sig 11. Solaris didn't bomb, it raised an error. And lets face it if you NEED speed you buy a bigger box, or more of them. I can scale Solaris to ridiculous proportions. How fast do you need it?
Solaris does have problems, most noteably that it is largely commercial, and expensive in that environment. But surely a free source approach to the OS, at least by opening the doors to adopt free source software into the Sun package will improve Solaris, and maybe some of the benefits will feed back to Linux. Maybe RedHat will release a version that works complete out of the box...?