It's come to my attention that the fast cast buff from inspiration doesn't follow normal fast cast rules in regards to recasts reduction.
BG wiki fast cast page said:
*Casting Time reduction cap is 80%.
**Thus, Fast Cast's maximum contribution to recast reduction is 40%.
Inspiration fast cast doesn't seem to follow this rule when used in conjunction with FC gear.
Did a test with 80% in fast cast gear, and 26% haste. No magic haste.
Ustusemi: Ni recast, 20 seconds.
Popped vallation with 5/5 merits and Futhark legs. + 60% fast cast.
Ustusemi: Ni recast, 10 seconds.
Since the recast contribution for fastcast should have been capped at 40%, due to the 80% FC cap, this should have done nothing.
Furthermore the change in recast is consistent with having 140 FC(or 70% recast reduction.)
base * haste * fc reduction
Test 1: 45*0.75*0.6=20.25
Test 2: 45*0.75*0.3=10.125
I welcome any corrections to my math, seeing as I didn't even realize that FC recast reduction was a separate step from haste reduction till I did this testing and the numbers didn't make sense. I thought you just added up all the reductions. /fail.
This would seem to imply that Inspiration breaks the fast cast cap, so I did a series of tests on casting time. Nothing intensive. I just added some code to my lua to record os time on the precast and aftercast of my spells then use those to give me a casting time. Going from 80% casting time reduction to 100% should be pretty noticeable I'd think.
After doing some control and inspiration up tests I couldn't see any difference between the two beyond normal packet jitter. I didn't record the cast time values, since it seemed pretty clear the casting time cap wasn't being exceeded.
Just to make sure the recast thing was something unique to inspiration and not a change to normal FC mechanics, I also did a short test on WHM/RDM. cast reraise with 80% FC and 19% haste for a 29 second recast. Added 14% more FC, but still got a 29 sec recast. So this does appear to be Inspiration specific.
My last test was to see if this would allow recasts to be reduced by more than 80%. Capped magic haste, kept 80% FC and 25% haste equipped. Under these conditions Ni recast was 9 seconds with and without Inspiration. So this does not exceed the global cap.
TLDR: Inspiration Fast Cast exceeds the normal recast reduction caps for Fast Cast.This does not apply to casting time caps, and cannot bypass the global recast reduction cap.
Basically what this means is that RUN can have very nearly capped recast reduction without any haste buffs at all. Or when you have Haste buffs, you don't have to use as much FC gear to get the same recast. This is particularly nice for enmity spells like flash and foil, as it lets you stack full enmity gear with no increase in recast time.