It's because you're running a sniper, and you appear to use it correctly. A typical sniper doesn't rush a spawn and look for kills, but rather sits back and lets his victims come to him

I ran overkill during last weekend when it was Double Gun XP in order to rank up two guns at once. I had a PP90M1 class where I just sort of rushed constantly and would just alternate guns. I also had a MSR/USAS class where I'd clear out my sniping spot with the USAS then snipe. I played much slower with that class

Short answer, it's your weapon choice that's slowing down your game, not the perk choice

I think you should just run AS50 and MP9 as a secondary. MP9 can compete with pretty much any primary in the game. This would free up your second perk slot for something MUCH more beneficial.

You might try using a sniper rifle with better mobility attributes like the MSR or the L118A with Overkill and see if that helps.

My best peice of advice regarding overkill-don't use it. I don't mean to sound like a d*ck if that's how it comes across, it's just that perks in this game can be very important and honestly there are some amazing secondaries in this game, but even more importantly you can pick peoples weapons up when you kill them. The majority of players only run the really good easy weapons like MP7, ACR etc... so chance are you're going to pick up great guns as well.

Also, don't forget that the secondaries (at least pistols and MP's) have the quickest swap times in the game, and for a reason. If you run overkill, you're going to increase your chances of getting killed during a slower weapon swap, or at least decrease the amount of time you can have on target due to having to use more cover etc... during the longer swaps.

The single MP9 ext. mags or silenced is an incredible little gun, amazing at range and rounds out almost any class well. For something you need to quickswap too, the 44. magnum, deagle, five 7, and the MP412, all akimbo, are very strong choices.