Since it's "upgrade" season, I decided to give Slic3r 1.2.9 another go. I was quickly reminded why I ran back to 1.1.7.

A problem many people encountered with 1.2.9 is best documented in this thread:

https://github.com/alexrj/Slic3r/issues/2960

There was a progression of solutions mentioned.

The first was to simply disable gap fill and thin wall detection in 1.2.9. This sorta helps, but produces other artifacts.

The next was to basically incorporate a high-resolution table of fudge factors into the gap fill calculations. This is implemented in the "stable" Slic3r branch, i.e., what is to become 1.2.10. So far, I've been happy with this (though building Slic3r is HIIIIIIlarious..., not.) I finally get the huge bump in slicing speed AND decent prints.

It appears that a more geometrically/mechanically correct solution is being developed for 1.3.0. I haven't decided whether or not to try building it yet because I have concerns that simply building it could actually impact the working 1.2.10 build somehow, thanks to the horrorshow that is the Perl module ecosystem. It may be that 1.2.10("stable") and 1.3.0("master") are sufficiently close to one another that they still have the exact same dependencies..., just not in the mood to find out at the moment...

So..., I mention this to simply let folks know that Slic3r may become a more viable option once 1.2.10 is released, and that the stable branch is useable should you wish to build it yourself.