Lew, Harvey recommended 10k to 15k resistance, and 1000pF to 1mF (!) capacitance, using .33mF himself. But every Decca was different. There was a device named the "Decade Capacitance Box" that would allow capacitance to be adjusted; with it you found the sound you wanted, and you would then install capacitors in your pre-amp of the value you decided upon.
A Decca/London is never going to be as refined or delicate as some, but, just like everything else in Hi-Fi, each listener has to determine what aspects of reproduced sound are most responsible for a satisfying musical experience. To me, there is the Decca, and then there is everything else. My friend Brooks Berdan would just shake his head and smile when the subject came up! They can sound rather brash, but part of that is because they put so much mechanical energy back into the arm, they reveal any weakness in an arm's bearings or the arm tubes stiffness and resonance. That's true of all low-compliance cartridges, though. The change to a line-contact stylus profile starting with the Super Gold helped with tracking, but that is still a concern. I completely understand a person's misgivings and apprehensions about Decca/Londons, and they really aren't for everyone. But they make music sound so much more like live music (which IS brash!) than anything else, I just can't quit her!