Mod...3/4 inch has 4500 lbs. higher breaking strength than 5/8 in 3 strand nylon. If you have trouble dealing with 3/4 inch 3 strand then I would suggest spending a bit more and getting 3/4 inch double-braid nylon which is MUCH softer and more supple and easier to tie AND even provides more breaking strength. 5/8" is just not enough for your boat.
... I know you can do about .30 cents a foot bettr on the price but I think sailnet will match prices.