If you don't have the manual for the boiler, Weil Mc has manuals you can view/download from their website. The manual should indicate the nozzle size if I remember. I have a mode P468V, which is a 4 section cast iron, and have a 0.75 80 degree hollow nozzle in it. The max nozzle size on my boiler' s name plate is 1.25. when I had a 1.0 or larger nozzle in it, the recovery time was rather quick, and the boiler short cycled. If I rmember correctly, my boiler nameplate is also a big number, like 150K Btu.
Oil's not cheap like it used to be, and I use quite a bit each heating season too
There are boiler experts here who will give you good info here though