How to drive a SPI bus over 5 feet of 26AWG wire?
How about this: you drive a current through the wire, that goes through the LED of an optocoupler on the other side. You drive the LED from the 3V3 supply, and the phototransistor in the opamp from the 5V. This solves two problems: The 3V3 to 5V conversion, and the sensitivity to external noise.