Nice thread.
For me, the need to upgrade is slowly diminishing with each change I've made. It was even a push for me to change from T3 to T4, and now that I have, the T4 has everything I want and beyond, I can't see myself changing my TOTL model in a hurry. It sounds wonderful and I can't fault it, so if there were no more arrangers available it wouldn't really bother me too much for this line.
The S950 however is almost perfect but I just wished it had better choirs and vocals, I am pretty sure the next S model will have these and that would probably be the only upgrade I'd need in that range (unless Yamaha release a choir pack for the S950).
We are lucky to have such fantastic instruments and you can't really go wrong whichever keyboard you buy.
Danny,
I think you are spot on the T4 will take some pull away to change and the better they get the more you are less likely to swap up one.
You do know that your closing quote " We are lucky to have such fantastic instruments and you can't really go wrong whichever keyboard you buy." I can here someone loading up the 50 mm cannon on the Messerschmitt 109 and he will be on your tail any-time now, he just needs to log a flight plan, daga daga daga daga, he'll be all over you like a rash