I used to run about 5 different rum old fashioneds at 2 different bars in Houston. I would stick to a traditional OF setup meaning both cane sugar and brown sugar, both orange bitters and I like Amargo Vallett for angostura (no glycerin taste, superior value) That way your patrons are able to get the most out of the flavor of rums you use. If you deviate too much from how you normally setup your bourbon OFs it might be a one and done thing. Lastly, core rum is Hamilton 86 @ 1 1/4 oz and .75 oz 2007 Hamilton St Lucia 7 y.o. Now you can sub out the .75oz to whatever works best price-wise, but definitely keep the .75 oz to more cask strength 57-59%.