Never kept a corkscrew, but I keep RFAs and BTAs together in a 20G. Not entirely sold that they're playing nicely, TBH. 6/8 of my RFAs have survived and are thriving (two arrived in poor condition and did not make it long past acclimation). 3/4 of my BTAs have survived and are thriving. BTA #4, which was of course the most expensive and my favorite thing in the tank, had one of the RFAs climb right up underneath it, sting it, send it into hiding, and ultimately it died on the back side of my rock where I couldn't reach it. Shocked me that the RFA won when up against a BTA. And of course that RFA hasn't budged since it claimed its victory spot in the tank. I have one other RFA that moves a lot and gives me heart palpitations over its proximity to my plate coral. All of the rest of them stay exactly where they were originally put.
I think whether you can mix really is going to depend on your tolerance for loss. I got great deals on my RFAs and 2 of my BTAs, so I was comfortable with rolling the dice. And note that it was my most expensive one I ended up losing as a direct result of mixing. But everything seems to have settled down now, and I'm pretty happy with the mix. If I were doing it over again, I would have worked my rockscape a little differently to try to keep the RFAs from climbing into BTA territory. With the Evo 5 you'll be challenged for space, so I'd put a lot of thought into your scape to try to create zones of separation that will be unappealing for the nems to cross.
