Update your Scorch to the latest firmware - but select Black Ops (even if you don't play it anymore).
Go into setup, and make right click the left trigger, middle = RB, and L2 = RS.
In MW3 (and other games) set the sensitivity to maximum.
Tactical is a better control scheme for CoD multiplayer.
Now you will need to turn the Scorch's sensitivity down until the screen just stops turning - if you've tried this before you will know what I mean.
Now you are ready to play. The reason I said use the Black Ops firmware as it has a more accurate deadzone for insane sensitivity. I've tried standard and MW2 firmwares but the deadzone isn't quite right for microaims and if you adjust it one click, it becomes too much for insane. Black Ops is just right - the reason for this is because the deadzone was made more accurate on Black Ops for thumbsticks(tiny bit bigger than MW2) but MW3 still uses the MW2 deadzone.
I've played with the Scorch for a long time and I am always trying to improve my skills, but I have settled with these settings for all first person shooters. Let me know you're feedback and any possible improvements.