Idea was drugs, and BTLs to empower him to insane levels of nasty. Do BTLs, and drugs go over the maximum attribute ? As in can I get to 13 using Berserker BTLs, Kamikaze, and the Narco implant ?
No. +4 is the max, doesn't matter how you get +4, but you stop there. The one exception I can think of off the top of my head is Wired Reflexes and Reaction Enhancers with the Wireless bonus as it specifically states you can go over the +4 Max.
And watch your Stacking rules, lots of things don't stack with other things. And keep in mind drugs don't kick in until the start of the next turn at the soonest so if you don't have any prep time, you won't be amped up. Cram, Pysche, Betameth, Novacoke ect are all excellent long term boosts that you can fire and forget for most of a session.