Hi Al,
long time no see or hear. Pleased your still around though. Dark Mantis fell by the wayside, quite sometime ago but I'm still here, throwing by two bits worth in, where appropriate.
The cheaper option would be to get 4 x 16Gb sticks to get your 64Gb of RAM. This is also probably the best way if you are anticipating going up to 128Gb in the future. Having never tried running this amount of RAM, I cannot say which way will work most efficiently. That said, I don't think there would be too much difference in performance, whichever way you go.