You might want to try the Sadowsky Round Wound Nickle strings. (Black SBN45B)
Prior to taking delivery of my RV5 this past November, I only played flats. I was looking for a brigher tone without sounding brassy and had my RV5 set up with the Black SBN45B strings. I've not looked back! I find that I can get a real bright funky slap tone or a very round fat punchy Motown tone, without sounding muddy, simply by adjusting the tone controls. In my opinion, these strings are certainly worth a try.