(in response to damogeans post)
A standard K04 will usually see between 295 and 305 bhp, or 360 if you provide your own bungee cord and stand WELL back
The limitations of Revo are that you have a sliding scale from 1-9 for timing, boost and fuelling and you are limited to this as you can't adjust a certain parameter against an rpm or throttle value, so it's 1-9 boost and that's that. What if you want the equivalent of 11 boost? Well you need to start again with stage 2 or 2+.
And you want to add boost at full throttle at 3000 rpm but not at 5000 rpm? Not possible. And you are getting timing pull at 3000 rpm but not at 6500 rpm so you remove timing to solve the problem at 3000 rpm but this also removes timing at 6500 rpm and the peak power is lower.
With a custom map in that situation you can remove timing at 3000rpm to resolve the timing pull issue and add some at 6500rpm, this allows you to have the best of both worlds. It's far more technical than that in reality but that's the basics behind the limitations and how a custom map overcomes these limitations to achieve the desired results.