You may want to AskTim™ before placing your order - the guy really knows its products.
Fixed that for you. Alt + 0153 is your ticket mate ;)
On the topic at hand: My vote is for the RR bridge. Thing with BKPs is that you always get multiple PUs that can do the same thing equally well, just in different ways.
It´s like you want a hearty meal to satisfy your hunger and you get a world class chef serving you 3 amazing hearty dishes which are all very different in ingredients. Now try to pick only one xD
When you got the RR bridge and wanne add a neck PU (with the finances being what they are you can hold up on that no problem, but in the long run I would say an upgrade there is worth it, you´d be suprised) the question you gotta again ask yourself is what do I want out of it with the Mule being that classic warm neck sound (but with amazing range) or the brighter more agressive classic neck sound that a RR will deliver.
Either way will leave you with a huge improvement and a grin on your face that will make your fellow musicians rather uncomfortable I suspect. Happens when I get new BKPs anyhow.
Cheers!