Am currently looking to upgrade my MC18R5 as well.

Was thinking Penske, for ride height adjustment (for the 17inch rear wheel change) and performance. It also seems slightly cheaper than the Ohlins from NZ

If I adapt something it will need a new spring and re valve anyway and will supposedly only be half as good.

The forks will be replaced with SP items with a re valve/new spring. To me the upside down issue is acedemic and the big diff should come from the cartridge.

After getting off my KR1s and NSR at the Taupo track and jumping on my brothers NSR400 with cartridge NC30 forks fitted, it was a huge difference.
Plush and planted versus skittery and no feel.