I heard somewhere that higher string Gauges such as 10 and 11 give a better sound for strats. So, what string gauge does Eric Johnson use? I read somewhere that he uses an 11 or a 10...

idk about EJ, but string guage is a totally personal thing. However the VERY generalized trend is the larger guage the better tone but harder to play. I've think SRV used 12's on his strat, but kept it tuned 1/2 down to ease off some of the extra tension
Check the GHS site. ghsstrings.com Eric Johnson has a signature set. One is 10-50 and the other is 11-52
2003 Music Man Axis Pacific Blue Burst