The more physical storage subsystem components, the better. Just a matter of logically using them so that their combined performance is additive, not subtractive to the workflow you have intended for them.
With 2x 2.5″ 7mm drive options available – I would be tempted to put aside any M.2 options we currently have available (if heat, and sustained speeds are concerns at all vs. a 2.5″ SSD option) and go for a 2.5″ SSD and a 2.5″ HDD.
The Hitachi Travelstars are the best you can get for the most balanced HDD option for the last decade or more.
With your torrenting biased workflow, consider two 1TB SSD’s (SanDisk Extreme Pro’s or Samsung 850 Pro) with a 30% OP on the O/S drive and a 50% OP on the data/torrent drive. You’ll need to have an external HDD to save the torrents to, but this setup won’t slow you down.