Hi guys I have never used wheel spacers and wondering what size to get?

its an 04 gtp and my summer setup is 20" msrs with 245/35/20 tires i believe. I don't know the hub bore of the rims but I do know that I didn't need to use hub centric rings when they were installed. They are also 5x114.3 pattern.

My question is how big can I go on the spacers ( i seem to have a ton of room on the lugs when I tighten them no spacers) and what size hub? Also should the spacers be 5x115 or 5x114.3 with my rim setup?

thanks