Serpentd..... Thankd for the kind words. He is just a bundle of joy.
Teehomo..... Yes, I think you will nead to come up on the oil if you have drilled out to 1.5mm
If you are running on smooth track, I would start out at 60wt, maybe going to 70wt. Don't be alarmed that your using such a thick oil. It will be fine. Just nead to make sure that the holes are free from "obstruction"
Bumpy track you may be ok with 60wt or maybe down to 50. Depending on how you like to run the car. (Stiff or soft, etc)
Viscosity will alter slightly with temperature. Another reason for running piston holes slightly larger than stock is that not so much heat is generated internally.
It is not alot.
EG: If you run 50wt at 70 degrees (20C) it would be around 55 to 60wt at 90 degrees (30C) Just a rough guide.
I hope this makes sence.
Menace