Sorry Mate,
I have no idea why I did that (3 hours sleep maybe), but you are correct, CS is on D53 and SCK on D52. Hardware SPI is working.
Interestingly enough, I just hooked up a second screen sharing MOSI and SCK with screen1, independent CS, RST and DC. they now both work when the Arduino is powered via USB (with one screen attached, it would turn white as soon as I plugged the Arduino into USB).
Cheers,
Fady