i think meron pa rin regardless of gain. the difference in tension makes your hand react differently with the strings. and apply the same picking strength to 9's as you would with 10's would definitely make the strings give off a slightly different sound.
playability vs tone "improvement"...
i've been contemplating on going 10s in this one guitar... i haven't played on 10s for maybe 8 years now... im tempted to go 10s for a fuller sound, but im sure playability will suffer a bit, and i might screw up on bending the strings on my other guitars (all 9s)... and of course, there's a risk of having to have my guitar set up again if i decide to move back to 9s... decisions... decisions...