What the Decca/London's need is not much gain (40dB is plenty) and lots of headroom. Their 5mV output is way too hot for lots of phono stages.
For solid state, the Liberty B2B-1 has both, John Atkinson finding it's overload margin about as high as he has ever measured. It retails for $1800 I believe.
For tube, the discontinued Herron VTPH-1mm is a great choice, providing 42-44dB gain (depending on tubes used) and pretty good headroom. Give Keith a call, as he sometimes has trade-ins available. You should be able to get one for $1500. The improved VTPH-2 will cost you more.
For the best performance from the Super Gold, you want to load the cartridge at 15k to 22k resistance, and 220pF of capacitance. The RB300 works pretty well with the cartridge, although an arm with a little higher mass and damping is preferable.