Was tinkering a bit over the last few days with Xjouve's excellent, big "Global Layer Mod & Co" (available under the mods thread) - and then I also revisited the big, total water map (ver. 1.1) that Xjouve released previously.
If you would like to increase FPS noticeably using the total water map, do the following:
a) download the total water map package ver. 1.1 (from the relevant mods. thread)
b) extract package
c) go into the OBDWW1 Over Flanders Fields/terrains/cfs3hyp (zipped) folder
d) toggle the "size" column of the cfs3hyp window to display file sizes, ordered from largest to smallest size
e) select all files from the biggest sized one (about 1400 KB or so), all the way down to the ones that are slightly above 270 KB in size, and then delete all of those files
f) this will leave available only 270 KB and smaller-sized files that follow the template-name "hyp00000x00000.cel"
g) the result is that a few larger bodies of water will be removed everywhere, as well as the flooding saturation way up above around Niewpoort and west of Ghistelles will be reduced (ave. FPS should jump up by about 20 or so this way)
h) you will still be left with tributaries, streams, several rivers, etc., including the flooding up north but in reduced form - better than no water mod. at all and no big hit on FPS this way
i) sizes in KB referenced above are for the files in zipped form, in the zipped cfs3hyp folder (no need to unzip before deleting the files with the sizes mentioned above)
Representative pics. below. Hope to get back into flying (and writing) the casual campaigns soon.
FPS maintained on approach to water concentrations
Fairly stable FPS again as we pass the flooding close to the coast up north (flooded areas slightly less prominent using my tips included in this post)
Some action around Niewpoort and the waterways but still no major drop in FPS
Below we are in the area around Lens, Bethune, etc., the good thing about this "lite" tweak of Xjouve total water ver. 1.1 is that there is not too much intersecting between the stock River Lys and other rivers/tributaries (the "lite" tweak of the water map works fine both with Xjouve's Global Layer package and also with stock WOFF terrain - pic below is with stock terrain)
Went for a drink and still fairly stable FPS maintained (even if FPS drop briefly with this "lite" tweak, they spool up again more quickly than if you install the full ver. of the 1.1 water map)
(Did not bother testing with the ver. 2.0 sub-theaters water maps since I find it more convenient now just to load my "lite" tweak of total water ver. 1.1. EDIT: have now tested the "lite" tweak as applied to the regional, ver. 2.0 water patches by Xjouve, and it doesn't improve FPS as much as when the tweak is applied to ver. 1.1 - if anything, most bodies of water disappear if the tweak is applied to ver. 2.0, with no benefit of higher fps. I therefore recommend applying the tweak only to ver. 1.1.)