Not playing much right now, waiting for 2.4, but when I was doing "speedruns", was doing 60s and yes, using rubies. I never finished the math, but "it felt" I was getting more exp/h than doing 65s. Remember I was doing non season and the lack of Bane of the Stricken made the RG VERY VERY long and that hurt my efficiency by a LOT. If u are doing season and RG goes down in a couple minutes, it might be better for u to do higher runs.

I was doing 60s in 9mins and getting 110-140 bil/h. I'm pretty sure going 55s or so would most likely give me more exp/h but I stopped doing exp before testing that.