Mast Tang installation

[mariner2k]

Hi, I am re-rigging a 50 plus foot round, hollow Sitka spruce mast. I will need and attaching point for the lower fore and aft shrouds and well as the intermediates. I've gotten some info from the Riggers Apprentice book, but I still have a question or two.
First which is stronger, a soft eye and thumbs cleat or a bolted and screwed mast tang?
Second, in the more likely event I use tangs, the book suggest bolting through the mast. My question regarding that, does it weaken the mast to any significant degree and is there a rule of thumb on bolt size to mast diameter?
Thanks, Kevin