I recently maxed out my class with the specialist kill streak in MW3. When I got 2 kills after my last perk, I got a "specialist bonus". Afterwards, I appeared to have sleight of hand(which wasn't one of my specialist perks). So what exactly does the specifialist bonus do? I've done this before but never noticed a real change and figured it was just for points. I didn't noticed I unlocked more perks
The specialist bonus is given when you achieve an 8 kill streak with the Specialist package (or 7 kill streak if you have Hardline).
It gives you all perks that you have unlocked (even if you have not chosen them as part of your package, and excepting Overkill), and all weapon proficiencies (except Impact, Breath, Damage, and Attachments). Check out the COD wiki for details.