I am having a difficult time deciding between a CP4 and S70 XS. I know they are quite different.

You should tell us a bit more about yourself or at least what you understand as the key differences.

They are both "Stage" products. One is a Stage Piano the other is a Stage Synth. The designation "stage" denotes an operating system that has an extensive real time accessibility. For example, creating Layers and Splits on the fly has been optimized to a degree that invites this activity. Sure, you can preset things, but you have real time access to splitting and layering on the spur of the moment.

The light that can be shown on this is.... one is the finest stage piano Yamaha has ever made, the other is a stage version of the finest Music Production synthesizer we've ever made. The CP4 Stage contains Yamaha's Spectral Component Modeling engine that covers the category that includes Acoustic pianos (CFX, CFIIIS, S6)- Electro-Acoustic piano (CP80 2 models) - Tine Electric piano (Rhodes 5 models) - Reed Electric piano (Wurlitzer 2 models). Programming here is building your principal keyboard sound with cutting edge processing.

The recreation of these instruments is done with seamless transitions throughout all velocities. And the entire signal path can be recreated with uncanny accuracy. The Components in the SCM technology include boutique mic modeling preamps for the acoustic pianos, and accurate recreations of the preamps of the various electric piano being physically modeled here. You can (re)build a 1973 Suitcase Rhodes (you can choose that preamp) you can adjust the strike position of the hammers... Or you can combine components to construct a custome Rhodes ... Mixing and matching preamps from different models. The modeling includes the Insertion Effects... Yamaha's Virtual Circuitry Modeling effects recreate all the classic sounds from every era. Vintage Phase Shifters, Wah Pedals, Flangers, mono and stereo delays, etc., etc., are available. (Some 400+ synth sounds from the Motif)

The S90 XS/S70 XS are Stage synths that are the top-of-the-line Motif series engine sans the sequencing and sampling recorders. It is able to load Motif-series Voices and Arpeggio data through to the Motif XS. So the synth engine and Voice compatibility withe XS, make the stage version of this engine a formidable choice. It also has programmable VCM effects and EQ.

The KEYBED actions are different. One is the best we make for electronic pianos (triple sensor, natural wood, Ivorite key tops, Granded Hammer 3) and the the other is our top-of-the-line Balanced Hammer synth action w/Aftertouch.

A survey will not help you decide if the 'shoes' fit YOUR feet. They are your feet. You have to decide if you need a piano or a synth. If most of your gig can be covered with a piano, electric piano, you will be extremely happy with the nice variety of ancillary sounds included in the CP4 Stage... Leads, pads, organs, strings, brass etc. The 76 Balanced Hammer action of the 70 XS gives you the basic Motif XS Library of sounds (1100+ sounds)

Your survey will only tell you how many lean toward a piano versus a synth. The two exist because these are two distinct customer bases. Either way you get a great keyboard.
🙂