110 string for the E is pretty good for drop D tuning. I use the Rotosound Billy Sheehan signature set which are 43-65-80-110. They feel nicely balanced and not too dissimilar to a set of standard 45's
Also, have a look at the hipshot D-tuner. If you're regularly switching tuning for half your set, this little device is invaluable.
Attitude II SFG; RBX-JM2; Att Std; Thumb 5 BO; Corvette Std fretless; LMII; MB 121H; Nova Dynamics; EBS Billy Sheehan; BEQ(x2); Mooer ABY; LS2; Mooer FOG; MS-60B; PT Jnr.