Elevation if anything gives you more fuel system since the turbo runs out of air faster than at a higher air presure. The Pure 700 has enough air flow to max out the oem fuel system on pump fuel alone. But some people do tune them with E25-30 just to get a bit more octane and run very low boost levels with higher timing.Are you going with port injection to run the e50 on the pure? I noticed you work with Payn Performance on your tune. Not sure if you're near Colorado.
I live in a high elevation area out in New Mexico. I am interested in going pure700 + e50. I fear I'd run out of fuel without port injection though on the pure at elevation.