S-950 is all I need,..........  

 but I will certainly look at the T-5 & what it can do...you think the NEW  T5 styles will work on T4/S950...? 
The S950 is a real gem, for sure. Hard to say if Tyros5 styles will be downwardly compatible...it may depend, not on new SA/SA2 voices, but what new 
Mega Voices are being used. It's much easier to swap in another SA/SA2 Voice than it is to find a compatible mega, at least in my experience.
How did the Tyros4 styles work in your S950 Donny? Did you get the raw T4 styles, or ones that were converted?
 Ian