I've been using 1+1 the last few months, is pretty smooth and seems to give an extra surge close to 4000 rpm which is fun! Was on 3+1 prior to that, I'll have to change back at some point to compare.
I don't use anything higher than +1 as I think this is the safest level for the car to avoid engine lights and what not - although you may be fine of course, it's just what DTUK tend to advise.