It depends what you're going to do with it. 100' of 3/4" stablebraid is 4 lbs. heavier than 100' of 5/8". Doesn't seem like much but if you're dragging it around up in a tree it can make a difference. We never use anything bigger than 5/8" but if you're forced to rig heavier loads you have to use the proper line. I'd rather rig lighter and work a little longer.
Just my preference,
Phil
I recently bought a 200' hank of 9/16 Stable Braid. It has a tensile strength of 13,000 lbs and has done all it has asked to do. I would not mind owning a 300' piece of 5/8 for pulling big trees even though I would only use it a few times each year.
You need to give more information about what you will use your bull rope for if you want a more detailed answer.
I bought 150 foot hank of 7/8 Samson stable braid. I haven't gotten to use it yet. I would say I overdid it. This stuff is heavy. On the plus side is has a breaking strength of 30,000 lbs. I got it for $120 with shipping but again it's too big! I'll keep it though. Basically it will be good to hook on the winch to pull trees over. I tied a Bowline in it and could not even get it set. I suppose loaded it will work.