Aye, these days, 9.8mm is a workhorse rope.
9.4/9.5mm is good all rounder; robust enough for the working stage of an RP campaign, thin enough for the proper RP attempts.
9.2mm and below are for sponsored heroes and desperate souls, in despair of ever ticking their project, and a week away from cutting the labels off their clothes and popping pre-session Dulcolax!
I really like the Sterling 9.4mm Ion Fusions, really low drag but hard wearing, but I think they might have been discontinued (replaced with a 9.5mm and a 9.2mm).
Also, one thing to note is that the diameters of ropes, or at least how thick they feel, often seem non-standard even within the same manufacturer. A friend bought a 9.2mm Sterling, as an upgrade on his 9.4mm Sterling but the 9.2mm was grabbier and more draggy. Possibly, as the 9.4mm was part of the high performance "Fusion" range and had a nicer sheath construction than the coarser 9.2mm, which was part of the more all-rounder "Evolution" range.