well did some testing last night and it turns out the magic haste cap of 43.75% is only the net magic haste cap, not the gross magic haste cap.
I found this out by being weakened and casting reraise on RDM/WHM with 25% gear haste, 80% FC, haste2, and SV double march with ghorn + hands. My reraise recast was 30 seconds with all those buffs.
weakness gives -1024/1024 magic slow.
reraise has a base normal 60second recast without being weakened and not counting FC.
SV x2 march is 640/1024 magic haste
haste2 is 300/1024 magic haste
gear haste is 256/1024 equipment haste
total haste then is 1,196/1,024
Maths:
x=expected recast time if magic haste is not being capped
Fast Cast = 40% recast
60s*[(1,024-1,196 + 1,024)/1,024]*(1-.4)= x ---- the +1,024 is the -1024/1024 slow
60s(.83203125)(.6)=x
29.953125=x
I had a recast of 30seconds. So as you can see, I did indeed have 94% magic haste.
Lesson Learned: if weakened, load up on that magic haste.