I'm sure there will be a SW 2005 SP5.0. SW typically supports the previous release with a one or two more service packs after the newest release is out. It would follow suit if SW 2006 was out and then SW 2005 SP5.0 were released.
I went straight for the download section on the subscription page. But only SW2005 SP 4.0 is the highest version.
There are two announcement of 2006. But the lowest on the page links to the EV subscribe page, the other links to the download page. I do not see any 2006 for download there?