For my 6 amp QSI Titan Magnum decoders in the tender I use a Cordless Renovations 4-Pin Aristo Style JST Quick Connector for track power (1 wire), motor (2 wires) and +5 VDC common to engine for lights 1 wire). The latter is to cut down on wiring between engine and tender. All of the lights in the engine are tied to this common.
Then I use a combination of Miniatronics 2,3 or 4 pin mini micro connector(s) for the other part of the light circuits and speaker(s) in the boiler.
The Cordless Renovations connector is kinda clunky but certainly will handle lots of amperage. I trim off the locking tabs and file down the sharp edges, etc. On one engine where I had to cut a hole in the front of the tender anyway for the tether(s) I made it big enough to partially push the CR connector into the tender.
With these connectors I get pretty darn good close coupling between engine and tender. Tight enough to just negotiate my 64 inch min radii curves. The connectors are not the determining factor. The tender front and engine cab and piping are the determining factor.