Okay, right now I am using Beefy Slinky's and i have to say I don't really like them. I love the guage, and I like the way they play. They don't stay in tune (could be partially my fault, had some issues when restringing), but what i hate the most... they have HORRIBLE harmonics. So, this leads to me question. Are there ANY other strings that come in .11-.54 gauge set? I can't seem to find anything.
d'addarios...been using their 11's since 1999 for my strat...10's for my LP and 9's for SG

Try the Blue Steel medium gauge. They are my favorite
yer i cant find a type that matches that set either becuase i was going to get them when i got my guitar setup and deceded against it and got dean markleys and changed them to boomers when i got it back.

i suggest you get boomers and do a bit of twiking.
Feelin the Blues

"The Blues are a simple music and I'm a simple man. But the Blues aren't a science, the Blues can't be broken down like a mathematics. The Blues are a mystery, and mysteries are never as simple as they look" - BB King
Ive used 11-54 before i went down to 10-52 and can't go to anything else. And DR strings are the best. But if you are going out of tune more than normal, it probably isn't the strings. Your tuners could be loose check your bridge too.