The speed is servo transit (turning) 60 degrees in seconds. Note whether this is 4.8V or 6.0V, they directly correlate
0.23 is slow, 0.15 is fast for offroad. 0.06 (JR 9000s) is blistering. I run a 0.08 speed Hitec Digital for touring car onroad and a 0.15 for offroad.
Offroad, torque is more important. 40 is low, 80 is borderline even for stadium truck, 120 is better, ok for 10th scale. 80 might be ok for a 10th scale buggy. Monster trucks need 200 or more, 320 is even better.
If you don't have enough torque, the vehicle will not steer or will not go the way you think when you're under load, bouncing around. Too slow and you may find it is not responsive enough for you.
Prices: think of it this way. There are about 3 price ranges to consider: $40-$50 bucks, $80-90 bucks and $120-150 bucks. $40-50 will get you a Hitec 645, not very fast but good torque about 100, will work for steering for 10th scale electric or nitro, not too expensive. $85 will get you a Hitec digital 6000 series (high speed 0.08, torque about 120) which is what I have in my touring car. $115 will get you a JR 9000s (0.06 speed) or 9000T (320 torque) which if I buy again will be what I get 9000s for onroad and 9000T for offroad.
I am most familiar with these, but check www.hitecrcd.com
and check specs. I go there first because Hitec has cheapest prices, then compare other models. People here running offroad seem to either go cheap Hitec or better drives go JR and are not disappointed.
If you check web sites you will find recommendations for torque/speed for various applications. I can't remember where I saw a table for this, but it was probably Hitec or Futaba site, or maybe Tower Hobbies.
Hope this helps.