R33GTRkid,
Flat 12 here with R32GTR and about 300rwhp. road tyres.
Dyno sheets are obviously a relative power figure for sitting on the rollers somewhere at a particular time. Power generation can change for a variety of reasons once arriving at a race track. The key to the tune is ensuring consistancy, road tunes are worth the time but, so is ensuring you are dyno tuning with the bonnet down and have basics like cold air induction in place.
Nothing wrong with x-speeds dyno , the numbers are probably right (bonnet up or down figure?). The car was just having some problems on the day.
GT-SS setup right are a high 10 turbo / low 11 no dramas.
You were missing a few ponies at the track, perhaps due to heat soak issues in the staging area as you mentioned. No cold air/exposed pods is a big part of that.
Hope that helps