Beautiful rifle Naki. It's always great to see that someone has ressurected an old classic.
I was interested to hear about your experience with the Lapua bullets. My first 9.3x62 was put together on a Howa action. I remember when we started trying loads, that it liked IMR 4064, but interestingly enough, just as you found, I could propel a 286grn Norma Plastic Pointed Dual-Core faster than a Speer 270grner. Who know's why? We couldn't figure it out. Jacket consistency? Just goes to show that it's worth testing your guns out and trying new loads!