I recently found out that members of the local MX5/Miata Club can get a discount on Simons exhaust system from http://www.auto-supply.no/ . I decided to buy the single tip version.

The system has 2.5" piping all the way from the cat and back and will hopefully decreases back pressure = lower exhaust temp + better flow and spool up.
I don't think it was designed for 94+ MX5 as it keeps bumping into the extra braces in the rear sub frame in tight corners. The 89-93 I.6 does not have the extra bracing in these parts.
The ass dyno tells me that the turbo is working more efficient now. I immediately got 0.15 bar more boost and it pulls noticeably harder above 5K rpm.
I have not decided if I shall turn down the boost or keep running it on 0.55 bar.
I'm really pushing the stock injectors now and knock can be hard to detect without a knock sensor.