Sensor, ADC, SPI master placement - 1 meter distance with 4 MHz speeds
Longer cable distances do not imply noise unless:  


The cable is picking up RFI (shielded cables help mitigate this)   
There is additional crosstalk from mutual inductance between the conductors of the cable. (really depends on the cable, conductor size and distance and wiring scheme)   
Your return current from both analog and signal ground has a common ground and creates common mode noise (a ground plane has low resistance compared to a cable)


I personally would just start building cables, do a short one and test the noise. Then test with a long one, if the noise is more than you need to start looking into the described effects and redesign the cable. It might also be advantageous to put the voltage reference and LDO with the ADC on the end of the cable.