If you have oxen feet (like I do) White's makes an FF (which is an EE. You'll notice their widths go: E, EE, F,FF.
They told me that F=EE and FF=EEEE.)
If you are wearing 10.5 and 11 in other boots, I wouldn't go to an 11.5. I feel they run a smidge long. My guess is that a 10.5 FF would work for you. Trace your feet. Either mail them in, or break out a ruler and see where you fall.
If you have EEEs that took some break in, you should check out White's in an FF. I hear so many people talking about rough break-in. My two pairs of Whites didn't need any break in at all. A well fitting shoe or boot really shouldn't take much break in. My feeling is that many people buy D width because they are used to buying off the rack shoes that only come in D width. But they probably have E or EE feet and don't know it.
This is from Wesco, not White's, but it is a good table to get an idea of how widths and sizes go together.
My feet measure size 9 and are 4.5" wide, which is off this chart. I ran it by Kyle and Bakers and he agreed that FF was the size to go for me.