I would say the following:
RLPL Savile - Classic fit TTS. No custom fit variant AFAIK
RLPL Drake - Slimmer fit, drop 6, sometimes pleated trousers. Similar fit to RLBL with a classic fit trouser and less padded shoulder
RLPL Drake Custom Fit - Much slimmer fit, best to size up. Custom Fit label inside jacket. Flat front trousers
PRL Custom Fit - Soft shoulder, very slim fitting, best to size up.