Suggested power tubes for Onix SP3 integrated amp?

Hello- I finally dialed in all of the minitubes for my SP3, a combination of vintage RCA's and Amperex 6922's. Now I'd like to upgrade from the stock Melody 5881 power tubes to something better. SED 'flying c" 6L6GC's and VA 350B's are under consideration, but honestly I'm not sure what's worked for others out there and the 6L6 universe is pretty foreign to me. Any suggestions?
Thanks for the help!