I currently have a mufflerectomy from the cat back, is it safe to run a decat aswell on standard map?

The theoretical problem is that the reduced back-pressure will cause turbo issues. It might, it might not. Personally, I wouldn't risk it when all the reports I've seen show little or no performance gains unless the car is maxed out in all other areas. I'd give Ben a ring at Shark Performance and ask his advice before I bought the cat delete (they are Miltek agents, so he could almost certainly do you a deal on a pipe and a remap).