We've just upgraded our Sandbox instance to Moodle v2.6.1 and are testing. These are some initial observations.
I've done a few test restores (admittedly using some very large course archive files*) and my restore progress bar never reaches 100%. It stalls at 99.6% for a while and eventually the "in progress" twirly in the browser stops. I don't get a "Continue" button as expected.
However it appears that the course is actually completely restored -- well, it doesn't generate a "Course restoration in progress" course. The restored course does actually open and appears to be complete. I haven't done a detailed content comparison yet.
I like the new progress bar, but the estimated number of seconds is entirely bogus. The last restore I did estimated something in the neighbourhood of 18000+ seconds at one point, but took more like 90. Amusing, but hardly useful.
So far it doesn't feel like the restore is taking longer than in our previous version -- Moodle v2.4.
* More testing is, of course, in the plan.