RE: epoxy strength vs cure time
Yep.
Like most modelers, I've used the hobby store-type 5, 10, 15, 30-minute epoxies from time to time. No denying that if you're in a hurry, they're convenient. But they are completely different chemically, and even the best ones i've used are inferior to longer cure (laminating) resins. I do like the ZAP laminating resin, although I don't use it anymore.
I've been using West Systems stuff for about 15 years, and you can really see the difference around the shop...
Mix any brand of 30-minute epoxy, use what you want, and leave the excess in the cup. (We use nylon cups, and re-use them when the resin is cured and will pop out.) As Bruce said, the faster epoxies will be very obviously more brittle.
Also, if you use the fast epoxies on a plane, just take a look at those joints after a few months. The resin is starting to change color, and often will shrink away from joints entirely. (and around glow fuel... even worse.)
The good laminating resins, on the other hand, make better joints, don't shrink as much, don't become brittle, and age much better. Today, I'd rather use a good epoxy and wait, than use the fast epoxy.