DaveW, there are many things about foot shape that make me think the best thing to do is find a shop near location (period as listed in your info) and pay them a visit. My feet are not wide but many boots just don't fit my high arches well. I've tried on a few models that felt really wide to me. Others that I'm sure would never be wide enough for someone with EE. What boots do you currently wear and are they worthy of just replacing? Call shops in advance to ensure they have several models in your approximate size, I'm sure that they won't disappoint by letting you try them on and walk around for a while. Good luck.
I'm an 11EE. Cabelas Guidewater Pro boots are Chota OEMd for about 60% of the cost of Chota RockLocs (but you have to tie your shoes bawling: ) and the Lacey store only stocked in EEE widths. I brought my waders and tried on a 12EEE and they easily fit over two pair of heavy wool sox plus the 7mm neoprene wader foot. They also snug up ok over a pair of med weight knee-high ski sox inside the waders for warm weather.
I have EEE's so I have the same issue. When Simms came out with the RiverTec boot I purchased several pairs as it was the first boot made that was comfortable in my actual size. Picked up several more pairs when they were discontinued and went on clearance so I'm the Imelda Marcos of wading boots but who knows when another EEEE boot is going to be made. You may still be able to find them on clearance somewhere (STP still has 7,8 for sale).
If you buy Simms do not oversize. I have a pair of size 11 Rivershed felt with hard bite screw in studs I would gladly trade for size 10 or L2 in a 10. I have thick insoles in them two pair of socks and I still cant lace them tight enough to stop the slop. Ohh did I mention they are wide. I have worn them 4 times.
I had the Freestone boots but the plastic lace eylets broke.