I've sailed last summer NP Heliums in all sizes on different sized JP X-Cite boards in Rhodes, when I was there on holidays (rental equipment).
It's a perfect combination.
The Heliums are very light and extremely early planing sails.
But no sail of 8.5 has the same power as one of 10.5. That's a fairy tale.
These sails also have less control in the upper wind range c/w racing sails.
It's for sure not the best sail for formula.
IS87 / IS101 / RRD114 / US147