On a tight course with short straights, you won't a big turbo becauase turbo lag and a very peaky power curve make it harder to accelerate while turning without losing your line or spinning out (RWD) ... A high NA Tune will be similar except without the lag, so it's a little easier to work with ...
As for stage 3 weight reduction, I don't think it's worth the cash unless you use that car regularly ...