[baakyocalder]

Well, the first thing you do in GURPS Mass Combat for determining TS score is determine what type of troops you have. Let's take your beholder and drow warriors as examples.

Beholder: Well, the beholder can fly through its levitation organ and has a variety of lethal attacks. Beholders have some armor, but their eyestalks are vulnerable and so are parts of their eyes. Looking at the special element types on page 6-7, it's pretty obvious that beholders are not armor, cavalry, C3I, artillery, naval, engineering, recon or transport in the setting. Beholders could be Air Combat, but Levitation isn't like a flight of pegasi or a dragon or djini or flying carpet, so I'll rule that out. Death rays, flesh to stone rays, disintegration rays and other attack rays of the beholder are nasty, but they may not be Fire given the ranges of Fireball and other direct damage spells. So, I'd go with Beholders as not being of any special unit class. For mobility, the beholder is basically on foot, though levitation makes him more mobile then a regular soldier, so Bob the Beholder and his fellow beholder warriors are probably Airborne like the airborne ninja on page 6 to reflect the ability of beholders to deploy in three dimensions. Or, you could call them Slow Air Mobility since they can travel for a long period of time with levitation, but not very fast. Hero or Supersoldier is a given. So, your beholders will then look at their armor for troop type. Per page 19 of Mass Combat, Flying Mages look pretty close, to beholders so start with a TS 5 per beholder and modify based on the beholder's AC and training.

Drow warrior: Well,the drow warrior is clearly some kind of infantry and maybe engineering or recon, depending on training. Light Infantry, which is TS 2, is a good base.

The key here is to look at your unit's general quality of gear, quality of training and abilities and pick what's closest to it. TS is a ballpark abstraction .. .