Someone came up with datamined figures for how much the monster hit points and damage dealt scaled up per each level of Greater Rift, which led another fan on Reddit to compile the figures in a big chart, running the math up to Greater Rift level 60. The figures are surprisingly simple, as it turns out:
The table can be seen to the right in jpg form. It’s a huge image, to click to see it in readable size, and click here for the document in a spreadsheet format. Note that these figures match very well with the player-observed Greater Rifticulty, where players have estimated about one difficulty level per 3 GRs, and estimated that GR25 = Torment 6.
Here are the actual figures, for the sake of nearly-identical comparison. Monster hit points increase by:
The figures also make it easy to see just how much the 50% damage reduction provided by the double Unity exploit is worth; approximately 4-5 Greater Rift levels. That’s just in terms of monster damage scaling, though, and you’d need to factor in monster hit points and your killing speed, since Grifts are a race against the clock.
How do these figures match with your observations? Going by this progression, GR28 = T7 and GR31 = T8, theoretically speaking. As most expert players feel that GR30+ is where things start to get really rewarding and requiring of very good gear, you have to wonder if we’ll see higher Torment levels added at some point. Well-geared character are now blasting through T6 Rifts, after all.