So comparing some of my guard units shooting would look something like this.
Assuming that the target is a Space Marine
Infantry squad:- ten lasgun shots
.5 x .3333 x .3333 x 10 = .5554 (therefore on average ten lasguns equals half a dead marine)
Ogryns:- thirty. ripergun shots
.5 x .6667 x .3333 x 30 = 3.3331 (therefore on average 10 riperguns x 3 shots equals 3 & a bit dead marines)
So on the face of this it looks like the Ogryns are the better choice over the Infantry Squad.
But this simple formula doesn't take points cost into account.
So I was just going to divide the Kills by points cost of the unit. But at the same time, my Google-Fu turned up Simhammer. This site is a treasure trove of info that works to simplify the "Mathhammer" of 40K. The Dakka Per Point (DPP) algorithm does exactly what I was trying to do and it gives a comparable value to the Resilience Per Point (RPP) algorithm. With these two values Simhammer goes a long way to creating a method of working out the efficiency of the units perhaps the last corner of the true-value triangle is movement, I am not sure how to work that one out. Simhammer also provide the algorithms in Excel format.
So if I run the same two units through the Simhammer algorithm this is what I get.
(To hit x to wound x failed save x failed feel no pain x number of shots) ÷ points cost x 1000
DPP Infantry squad
(.5 x .3333 x .3333 x 1 x 10) ÷ 50 x 1000 = 11.108
(.5 x .6667 x .3333 x 1 x 30)÷ 410 x 1000 = 8.130
So when shooting at marines, an infantry squad is more efficient then a squad of Ogryns. Even with the higher strength riper guns that produce three times the number shots of a infantry squad. The chunky Ogryns are just too expensive points wise.
Armed with these tools I was able to determine what units were the most efficient use of points in each force org slot.
Perhaps now with 7th edition out with its unbound army list rules, I could use the DPP and RPP algorithms to identify the most efficient unit in 40K and take a full army of just that unit.
I didn't even get to play one game of 6th Ed.