You can tune pretty much any turbo car to be peaky at different RPMs. Unitronic is probably one of the least aggressive tunes out there. If you have a map peaking near 30 PSI then your boost is going to taper hard near redline and power is going to fall off fast. There's a reason the fastest is20 cars are all shifting before 5500 RPM. If you're on a very mild tune then yes, it's possible that you make power all the way to redline. However you're sacrificing A LOT of what the is20 is capable of to do so. Here's a dyno sheet from my car:
http://www.golfmk7.com/forums/showthread.php?t=33914
Shifting right around 5300 RPM means I'm shifting right before the power/torque falls off hard and puts me in the next gear where there's a lot of torque. is20s don't make power when they're wound out to redline.