You've got all your bases covered IMO except for a 12x10. Be interesting to hear how the 8" BBS and 8" Tornado compare for you. Besides the BBS version being heavier, some say the Tornado is an all around better coil in pretty much every respect, though I hear the BBS version was prefered as deeper and a better coil than the old 10" BBS coil by some. If you can do some air tests between them that should be interesting. Also would like to hear how they both compare to the Seasearch, as that's an 8" coil ain't it?
Since you've got an 8" Tornado on the way, you might want to consider trading off that BBS and Seasearch (I think the Searsearch is 8"?), although I hear the Seasearch is a very stable coil and many liked it for land use even though it was heavy. I suspect people might have been prefering it before the Tornado came along maybe though. Don't know. I think those Seasearch coils only came on Excals and were only put on them very early on I think.
In my line up this is what it's going to be for every situation...
8" Tornado for when I want to work super heavy trash hard without as much need to re-grid from 90 degrees due to it's shorter length than the 12x10, though I'm very confident in the left/right separation abilitity of the 12x10 and don't see how it can get any better, and I mean that. Re-gridding from 90 degrees with the 12x10 and I doubt it'll miss much due to it's fantastic left/right separation with it's super sharp DD line width wise.
10" Tornado for water use only, though I bet when I get an S-12 it will replace it for that. Both being prefered in water over the 12x10 due to lower drag.
12x10 for every day land coil. I'm very confident/impressed with this coil in heavy trash, though length wise the 8" Tornado will help. The depth and stability of the 12x10 is also something to behold, and it has a very "crisp" and louder language over the 10" Tornado as well.
13" Ultimate for days I'm in the mood to use it as a different beast than my 12x10 in certain traits, or for sure when wanting to grid out large open areas faster, although the 12x10 is still an improvement in that respect too over the 10" Tornado. Just that the Ultimate makes coverage even easier. Both it and the 12x10 are my go to deep coils, though they are still both impressive at left/right separation and also coins on edge. The Ultimate has an even louder voice than the 12x10, and also makes targets sound crisper in tone like the 12x10 does. Both fantastic coils I feel every Sovereign owner should own without a doubt.
Once I get a 8" Tornado for working super heavy trash hard, the 13" Ultimate to replace my loaner, and an S-12 for intended water use, that will complete my line up. With the S-12 in hand I might even trade off my 10" Tornado, as it will no longer have a use for me, since I'll never use it in place of my 12x10 on land or in water over the S-12 anymore. That is, if the S-12 doesn't create too much drag in the water like my 12x10 does, but I suspect it won't being round in shape. Still looking to trade off the S-5 for an 8" Tornado or Ultimate. If anybody wants to make that trade shoot me a PM. The S-5 is in good shape and they are $200 coils.
The only other coil I'd personaly consider is the 15x12. I owned one for a while. Not as deep as the 12x10 or even the 10" Tornado on coin/ring sized targets in my soil due to my minerals I suspect. It is one very stable and fantastic coil though with awesome coverage. Even better coverage in some ways than the Ultimate, as the Ultimate is only 12 & 1/2" in actual length while the SEF is 15" length wise. Length is where coverage counts in a DD, as the DD line acts like a wiper blade as you sweep. But, the true 13" width of the Ultimate does make it easier in that respect to cover stuff to your right or left as you sweep, so between them it's a trade off in one respect of coverage to the other in a way. But, being 13" wide, the Ultimate only has a half inch more coverage at the end of every sweep if you think about it that way. Also, the squarish shape of the SEF makes it wider over more of it's length. Still, I seem to find the Ultimate easier to "paint" the unswept ground in front of me easier without as much need to hold my steps back as the 15x12. The Ultimate is also a good bit lighter and feels better on the shaft IMO over the 15x12.
I would recommend anybody wanting a larger coil for more coverage to opt for the Ultimate if weight is primary, or opt for the SEF 15x12 if stability is primary due to either EMI or ground minerals. That is how I would decide between those two coils. The Ultimate is still a very stable coil for it's size, but the SEFs often allow higher sensitivity settings, slightly less chatter, and less nulling in some situations. Both are excellent coils in many respects, with the only contrast to me being weight (the 15x12 is still lighter than the 10" Tornado though if you remove it's coil cover), stability in EMI or bad minerals, and just in general the "feel" of the Ultimate being more "right" on the shaft. Might also be the Ultimate is deeper than the 10" Tornado in my soil (don't know yet) where as the 15x12 didn't appear to be for my minerals.