First time I have read this thread and at first thought you had an edition 30 then realised you had a k03 gti. Do you really think a ko3 even with stage 2 + is gonna get to 300bhp. I would be inclined to think that the dyno your using is being abit over generous with the figures.max stage 2 + ko3 real life figures would be between 270 and 280 bhp,and that's me being generous myself. 
To be honest I'm not 100% sure, although I think so.
My best friend has had his Civic Type-R rolled at the same place as me and he was complaining it was giving off stingy readings.
Apparently his Civic managed 310bhp on Celtic Tuning's RR and yet he only managed 296bhp on MB Motorsports RR, the same place where I had mine dyno'd.
Also an apprentice who I know, and who works at a local garage near me claims his Renault 5, only made 169bhp at MB Motorsports and yet it made 181bhp at Alan Jeffrey's in Plymouth. And let me tell you if you don;t already know. Alan Jeffrey's is notorious for stingy readings

I have had
two dyno's done on my car now, taking into account only my performance mods (IC/TBE/INDUCTION/DV) and with only the standard map of the Gti. One reading made 229bhp (At Alan 'Stingy' Jeffrey's) and the other was 234bhp.
So if you're asking will a decent re-mapper be able to eek 65-70bhp out of the KO3, by adjusting the boost levels, then yeah I suppose so. A KO3 can and probably will turn the 300bhp mark

After all my turbo won't even hold boost much more than 15psi after about 4 grand. So hopefully once rectified, the extra bhp can be realised.