Hi @rpsimon ,
In terms of run time for reports, you're likely to find that Test will not perform any better than Beta, and could be even slower. There are some unknown variables at play, like is someone else on the same AWS cluster as you running a lot of reports or sis imports on Beta, which would slow down your report generation but not doing the same on Test. As far as I know, Test is the least supported environment at this point, and new customers don't even get a Test instance anymore (just Production and Beta).
Can you share why you're attempting to run reports in the non-production environment to begin with? There are some one-off scenarios where I know that could be useful, but if you're building some kind of regular business process there might be a different approach you could take to try to work in Production. Let us know if you're able to!
-Chris