half x5.5 half DGS400

I have a dilema Discount Golf,My irons are DGS400 but i have always struggled to get distance from 7 iron to pw. The long irons go beautifully.so i tried a friends x-forged that had project x 5.5's. The 7 to pw went beautifully (and 5-8 metres longer which was like finding the missing link. The longer irons however didn't do any better Used Golf Site, in fact Used Golf, slightly less distance and higher flight.What's going on ?How common is a problem like this ?Taylormade Superdeep 8.5 degree RIP70 stiff909 F3 15 Voodoo StiffMizuno TP-19 3-PW (DGS400)Vokey SM 52 and 58RIFE Aussie Putter