899 is only 6 PY numbers shy of 905! Half way between 870 and 905 is about 890, in the range Chris suggests and I think Peter means, apart from a typing error! A PY of 890 implies that a new rules IC should complete an hours long race 54 seconds faster than an IC one design. I wonder if that was the sort of average gap between say, John Ellis and the two new rules boats at the Nationals? They were certainly more than that ahead of me in most races, but with so few boats it is hard to keep the 'crew skill factor' constant!
If you go for 890 and your club makes on line returns of race results as the year goes on, the RYA will give frequent feedback to the club as to what PY you should be sailing off either against Primary Number boats sailing at your club or against the most frequently sailed boats in your club handicap fleet
. However, this number may well be very different from the published PY for the class. Draycote where I sail was one of the first clubs to make returns in this way and the RYA comes back and tells us that ICs at the club (almost entirely my results) should be on a PY of about 926 on our inland waters. The trouble is that the most common 'comparator' boat in the Draycote fast handicap fleet is the RS300 (PY1000) which I never manage to beat by about 5 minutes and hour till the wind is about a force 4. In light winds the best RS300s are up with me on the water. It will need a lot of returns before the RYA will be able to generate a reliable number for the new rules boats and if just two of you do badly against better boats than ICs in light winds (like the RS300 or Phantoms) at your club, the PY for the new rules boats could turn out to be higher than 905!
Have fun off 890. Colin