Average All Damage. This is great with fire-arms. Just apply the 3.5 per d6. Do the same for melee weapons, but melee weapons have "/" where the maximum damage is placed. Margin of success if is additional damage. You really don't have to allow the extra damage for melee, since GURPS is pretty lethal.
Now that there is a more or less static value for damage, there is one less roll per attack. Use the Character's HP and the Wound Instances (HP/2, HP*2/3, HP, -HP etc...) into "Conditions" up to the number of conditions relevant to your game. So you have Wounded (HP1-4), Major Wound (HP/2), Crippled (HP*2/3), "Bloodied"(HP), Dead (HPx5). These conditions benchmark damage (damage after all DR modifiers). So if a character takes a HP worth of damage it is a wound that would Bloody him.
Track wounds by listing down the wounds like "Wound #dmg type" it can follow with the note location and special effect.
To speed up Combat, I'd replace Active Defense with a penalty to TDM. The math is off the cuff. What happens is the character choose an active defense, and the score determines penalty. You can roll before choosing the active defense, as long as the one choosing the active defense doesn't know the value of the attack roll.
Active Defense Score, TDM to Attack roll
Removing two points of reference should speed up the combat. The GM can set up some "defaults" like torso if no specific target is declared, best defense remaining or dodge if no defense declared. After the learning curve, combat becomes much faster.
No of Players
No of Units that make independent actions.
Units as part of a Group. Half minute per mook.
No of Exchanges (Players asking target nos. or clarifications)
No of rolls in the process. A Roll can add a minute worth of exchanges.
5 players, vs 20 mooks and 1 BB.
thats 6 people at about 6 mins per round worth of exchanges.
The GM handling 20 mooks can take extra long. That can take 10mins for the gm to resolve the mooks.
The GM does tactics and careful consideration of the BB, so he takes about a minute or two.
so far the total time per round is 18 mins per round. The mooks hit ability to hit determines the amount of time (% x 1 min). If they hit more than half the time, that means they are rolling damage at that same rate and trying to count beans. so if the mooks hit 30% the mooks may take about 3 mins to resolve. Making the round time 13 mins.
If they have a 90% to hit, then that means 90% of the time the GM is rolling damage. The GM is making about 18 more damage rolls and talkint to players telling their damage and all the other consequences.
as compared to
5 players, 3 followers (90%) vs 3 striker mooks (90%), 5 tank mooks (60%), 1 controler mook (90%),
6 people = 6 mins, 3 followers = 3mins, 3 strikers = 3mins, 5 tank mooks about 3mins, and controller about 2 mins. 17mins each round.
If this GURPS, resolving the round is about 50% more time because there about an extra roll. if you add the random hit location rules, thats about double the rolls. that would be 34mins for the second encounter.
Ideally with only one roll; it would be faster than a DND round by a small margin. with practice it would be half (9mins). Preventing rolls in the system can be remedied by creating Consumable Cards (see using cards article from way back).