OK, this looks like it's going to be a loooong post.

I agree that it would be best to wait until 6.1 before importing as I do run quite a large board and the importer is greatly improved as well. The rush to upgrade isn't that great as long as my web host can hold out (server resources are huge at the moment). Plus I'm paying for 1.5GB of transfer each day and if Threads can bring that down (even by 5-15%) then that would also be a big plus.
And now to the questions that have been accumulating in my head over the last hours...
1. Are most options, such as topic ratings or adding attachments, controlled (on/off) by directly toggling the template as opposed to doing the changes in the Threads control panel? For instance can I switch off the threaded view option in the control panel or must I remove it by changing the template itself?
2. Are post extras (such as 'Print Post' or 'Remind Me') toggled in the template as well?
3. If I apply a custom UBBC-style template in 6.1 then can I later revert to the standard one and use the UBB-skin as an optional template (once the multi-template feature becomes available)? I assume the answer is yes, but I thought I'd better ask just in case.
Just thought I'd add a shortlist of things I'm don't like in Threads as a UBBC user (would be great if some of these could be control-panel toggled one day):
- repeating the topic title in each post
- using "edit, reply...", links next to every post (don't people scroll all the way down to the last post anyway)?
- seeing only one post after clicking on reply as opposed to all posts on the page
- and the main one: TINY, TINY box/area to write the post (post message screen). Threads only has 5 lines whereas UBBC has 12 (I bet this is a really simple template alteration).
Overall I would like my users to feel as much at home as possible after the change (especially since I'm sure there'll be login issues, etc., to keep me busy). Thus the plan to use a UBBC template so that initially the change to Threads looks minimal from the stylistic perspective. Afterwards, once multi templates become available, I think it would be good to swing the other way but at the same time leave people the option to stick to the Classic look.