Speaking to some lad who swears he has run 250bhp on several different dynos on a standard turbo... I'm thinking BS. I even offered to race him in my stage 1, but it was an empty offer as I know it will never happen.
I only rant as 250bhp in a GTD would be the perfect amount of power imo and I would love that in mine.
I spoke to one of the top, most reputable tuners (won't name names) but everyone has heard of them. They reckon even with every mod possible you won't get above 220ish max! Unless of course you get a hybrid turbo. They have no reason to BS me, as they could have made money out of me... But, they were honest. Probably why they are the best.
You see all these wild claims on YouTube... but funnily enough, there are never any side by sides demoing this supposed extra 30bhp over a stage 1 map of 220bhp-ish.