No, I never used the MP40, other than my first Prestige up to the challenges, then I was done.
Because using the weapon makes you good at the game right? It means more than what you think it means; people that use OP weapons generally display personality traits that are undesirable. It shows what kind of person you are, really. If you like using OP weapons, it means that you don't care if you ruin something for everybody else, just for your own personal gain, which shows greed, and selfishness. I have no respect for people that do that. I don't care if anybody else thinks that I'm any better for not, becasue I know that it proves that I'm not a complete asshole who isn't considerate of what other people think/feel. That's the kind of person who would get a job, and do nothing but talk on their cell phone all day, while other people do all the work, but that's okay, they get fired eventually.
For instance, in BC2, I tried to use the worse weapon in the game, pump shotguns and the pistol. Then I found out pump-shotguns with slugs are OP, then I tried the AEK, but that's OP, along with the Grach, so towards the end, I was using the T88 with an M9 as a medic, and the F2000 and M9 without Magnum Ammo as assault.