Well, from that information, yours is a fair bit laggier. 1000rpm by the looks of it! Also, the power difference depends so much on alot of other things. What T28 is it for example? There are many variations.

Also, the tubular manifold may be negative at your level. There is a possibility that it isn't needed.

I have about 1-bar by 4000rpm on my current turbo (GT30), so I would say that there is something not right with yours.