1.17V wasn't stable after all - I got a BSOD when I tried to run more passes of IntelBurnTest. 1.18V seems better - 50 passes of IntelBurnTest at the maximum setting and closing in on 12 hours of Prime95 without any hiccups. The temperature peaked at 76C during IBT, and 68C during Prime95. I doubt I will see much above 60C during normal use, though, so that is totally fine.
I might replace the TIM if I get around to it. Perhaps I will look at replacing or adding a more efficient exhaust fan at the back, too.
Thanks for the replies! Makes me feel much more at ease about the mounting not being faulty.
EDIT: Haha, so just after making this post and browsing the web further while Prime'ing, I got a BSOD at 1.18V.
EDIT2: Idle temps are 31-34C with the front door open and all fans running at full speed. They are about 5C higher with the front door closed and all fans at 700-800RPM.
EDIT3: I actually found an old paste of AS5 *facepalm*. If I can be bothered, I might mount once more.
Seems like I missed the question about airflow the first time around, so to answer it; there doesn't seem to be very good airflow with the two stock fans - I haven't seen more than a 5C difference under any circumstances with the two case fans running at 1350RPM vs. ~800RPM (the bundled fan controller can't go lower than ~6V, as per SPCR's review - http://www.silentpcreview.com/article1192-page3.html
). The rear fan also seems a bit too audible and I would be open to suggestions for a replacement.