Naked Utsusemi Ni went from 45 to 42, Ichi from 30 to 28. Quick math on this makes it change recast by 6.6% which is pretty damn nice. I'm not sure what the change to casting speed actually is because that's harder to judge. Usually the way fast cast enhancements work though is that the reduction in casting time is 2x the % of the recast reduction...which would put it at 13.2% or so...idk...that seems way too good to be true since that would be higher than any other piece in game including RDM AF (but i guess the recast change of 6.6% is already higher than anything else).
Actually, that sounds like a 5% recast reduction (so 10% Fast Cast/5% recast). If it took the recast down to exactly 42 seconds (for Ni) then it wouldn't be 42 on screen long enough for you to register it. On the other hand, 45 * .95 = 42.75, and 30 * .95 = 28.5, which match the whole seconds values that you see. You may also want to test with higher recast spells such as Reraise (5% recast reduction would take it down to exactly 57 seconds, so you'll probably see 56 seconds, though you might see 57) and varying haste totals, though it shouldn't be too hard to pin down.