And in regards to custom made exhausts / headers,
Ive had a couple cat-back exhausts made for me (but have never had custom headers made for me).
Thus my opinion is purely based on my experiences with custom cat-backs.
And the result was that I was not satisfied both of the times.
Then I had decided to just go with 'branded' exhausts.

Personally the I don't really like custom made stuff based from my previous experiences.
The reason being that although you can request for something (low-end power gains), you don't really know what you're going to get until they have fabricated the system.
From the ones that I've gone to, they dont test or tune these obviously because it will be time consuming and costly, and hence cost you more.
Most times the best they can do (to get low-end gains) is fabricate one using a small-ish pipe diameter, mandrel bends and a straight through muffler, whilst at the same time ensuring that the piping bends complement the car (suspension clearances etc etc).
At this point in time all you can do is hope that you got what you wanted and paid for.

The reason that I do like 'branded' products is there is no guess work involved.
The research, testing and tuning is already done.
Most of them can show you (using dyno figures) what their exhaust is going to do for you, and particularly where the increase of power is going to be across the rev range.
For me personally, I am a fan of Toda headers.
They provide a quality product with proven performance.
But at the same time, yes, they are quite costly in comparison to other brands of headers and custom headers.
And I would be happy with those gains.
At the same time, I do agree with you TypeS.
Based on the dyno figure you have provided, although there is some overall gain across the rev range, gains are predominantly in the top end (excess of 5.5k rpms).

To the OP, it really comes down to what you are looking for.