Why this fascination with the superwing being somehow different to tune? It's not some kind of esoteric beast.. there are thousands of them out there.

The principles of tuning any mast hold true for the superwing, in fact it seems little different to the old IYE and, more particularly, Holt Allen Shearwater masts we used back in the early 70's.

The purpose of spreaders are two-fold. To support the mast laterally and to force pre-bend in fore and aft through rake. The further back you rake the spreaders, the less diamond tension required for a particular bend. Balance this against a slight loss in lateral support.

Little rake and loads of tension means that your mast is heavily loaded already and therefore downhaul will have greater effect in the top of the mast. More spreader rake and less tension for a given bend allows the downhaul to affect the whole mast more evenly. Banging on loads of diamond tension is an age old way of dealing with a real blow (but it limits your on the water options).

I too spent thousands of hours doing two and three boat tuning, comparing rake, pre-bend, sail draft, downhaul settings etc. I can echo what John P has said. The boats (Tornados) were not greatly different from each other except when we started to play with rotation (once pre-bend matched luff curve). This was where we could have the greatest influence on power and pointing.

In your position Eric, I'd follow John's advice. Then, bearing in mind the principles I've outlined above, use your own experience and intuition to fine tune to your boat and your sailing style. Never stray however from the unloaded pre-bend (however achieved) matching your mainsail luff-curve

Happy sailing and testing!