In SX Microcontrollers, SX/B Compiler and SX-Key Tool, George Herzog wrote:

SPI is intended for short distances [like inside the same chassis if not actually on the same board].  Speed is a consideration with any distance as transmission line losses and reflection of signals will come involved.

Having said that, the easiest system to impliment is 8 wire internet cable and connectors [RJ-45].  The parts are everywhere and cable is often shielded.  It still is a somewhat of a hack approach as you cannot really take advantage of the twisted pairs with SPI to reduce noise. But wire is wire and with SPI running at 100kHz or 400kHz maximum speed, it can be a good convienent resource.  If you want to run at Mhz, you may have trouble.

I suggest you buy a cable that is about twice your distance and test the SPI for reliablity with that.  If it works reliably at twice the distance, you should have little or no trouble in actual use unless you plan to have all items on the same SPI bus.  IN that case, distribution pattern needs to be considered.  Also there comes a question of having enough CS lines available for each device. For a shared bus, generally a star distribution pattern is the worst, while a daisy chain is best.

The easiest solution to resolving problems is to slow down your speed unti none exist.  SPI, unlike one-wire and I2C or One-wire, does not have an acknowledge signal to verify a byte is properly framed or other error verification scheme, so it is up to you to trap problems.

This points out the obvious, you might be better using One-wire or I2C.

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