With 98ron and the CHI's you can go as much as 11.5:1 possibly 12:1. I know you can go between 12->13:1 with a massive cam. A the huge it bleeds off the pressure.
I've ran 91ron in mine with the CHI's @ 11.2:1 static (185psi cranking pressure). Drove all the way to Bendigo (Heathcote) and back on it. Almost 500k's round trip.
Have you spoke to John @ CHI about cam selection. As quite a few people on these forums have stated. Off the shelf cams don't ideally suit the heads. John should be able to pick a suitable custom cam. It's even more difficult for you due to your windsor block. As windsors weren't known for their well breathing heads
You best cam will be a totally custom heads setup for the windsor block but taking into account the alloy heads.