Now a small disclaimer before I start spewing possible bull shit here.....
The revs and power curve of an engine is pretty much a combination of a few different things...
Firstly the ability of the engine to rotate at the required rpm, so balancing the overall displacement (bore and stroke) in the given number of cylinders to have the minimal amount of rotating masses thus limiting the internal forces involved and the engineering to keep it all together. This is why generally a large cc motor has a very low max rpm, as the cylinder capacity has to be quite large in both bore and stroke. But say an F1 engine spreads the 3l over 8 cylinders, and the stroke is very very short. So during each revolution the piston doesn't really move that far of a linear distance, meaning that it can rev like a b*stard. The higher the revs, the more power you can make...however torque on an F1 car is relatively low but it doesn't matter so much cause they weigh so little.
and secondly the VE of the engine at that rpm. So the ability of the design to suck air in, compress it and add fuel, ignite it and spit it out again...all at this higher rpm whilst still making a decent enough amount of bhp and torque.
Going back to the good old days, the normal way to change your power/torque curve was to slap in a new set of cams. This gave you a better optimised profile for high revving engines. Meaning the timing and lift of the valves were such that at this higher rpm range, the engine would happily be able to suck air in, and spit it out again even though it was rotating faster than originally designed to do. Ofcourse it then ran like a bag of shit on idle and up to say 4k rpm, but after that wahoo...on cam and off you go.
Then the VVT came in, to then optimise VE (volumetric efficiency) for both high and low rev ranges. Most using oil pressure to force the engine at a given trigger point to use a 3rd middle high lift cam profile during high rpm's. Honda VTEC and Renault are the ones I know the most about.
Now, given that you want to keep the engine internals standard, I would assume that you can remap it to give you the max power higher in the rev range, but this would effect your torque curve too...as you are essentially delaying the power delivery until a higher rpm is reached...then the engine won't be producing as much torque as it should and your power/torque curves would be very much reduced and spread over a narrower range.
What you are suggesting is keeping that torque and power the same but extending the range it is effective for. To do this, I would assume that you need a greater supply of air to the engine at higer revs to maintain its VE. So the turbo is the obvious component to change. You need to keep the balance between air in, mix fuel and air out. So a change in turbo alone will not give you a lot because all this is doing is increasing your ability to give your engine more air...you then need to be able to squirt in more fuel - need bigger injectors and more fuel pressure. After that you then need to get rid of the air more quickly too, so better exhaust.
Fooked if I know what this all means....but either way I don't think a simple re-map with standard internals will extend it a great deal. Just better optimise what you have already.
Now - where's my pint....