Anyone who thinks WoD is better for gains than Wildfire at 90, at least after scrolling up, skills needs to reduce their drug intake.
I just ran a test - I'm currently training Spellweaving, and was at 90.2 when I started today.
WOD. ONE gain from dozens of attempted castings, casting nothing but WoD to go with my RC fighting Swoop. As I'm not currently using a focus, the damage to swoop is minimal (until I get it below 100 health, which takes 3 RC castings), about what one would get from Wildfire, so the damage levels aren't throwing off the tests.
Wildfire. Multiple gains per Swoop, usually 2-3, in about the same number of WoD castings.
Now, the way most skills work, each 5 points of PS over 100 indicates an increase of 2.5 skill in the window of where gains are possible. It really only extends the top end, not the whole spectrum of gains. At 120 PS, that's a gain of 10 points. HOWEVER, that's still only an expansion of the very easy range, where gains are supposed to be difficult to come by. The speed of the gains I'm getting seems to indicate I'm still at a lower tier (after all, I'm still failing some castings, even after reaching 91 skill)
At MINIMUM, if the spells started with a 50% success chance, the skill gain window for Wildfire should be 25 skill, up to 91, for unscrolled. 101 for scrolled. The fact that I'm failing on castings (consecutive ones, even) now at 91.5 indicates this isn't the situation.
If the spells success chance starts at ZERO (like Magery - the lowest level spells for most casters, equivalent to level 1 & 2 mage spells, actually start with a negative minimum skill level to give a small amount of success chance at zero), that would be a 50 skill window, and gains would be possible to 116, or all the way to 120 if scrolled to 110 or greater.
If it starts at some other number (say, 25%) but progresses at the 2 cap/1 range ration, then the ranges below 100% are reduced accordingly (with the amount between 0 and the start number cut out), but the extensions to the top end remaining (for the hypothetical 25% start, Wildfire would start at 25% at 66 skill, and hit 100% at 103.5 (66+37.5), with power scrolls extending it another 2.5 to 10 points.
If the window is something other than the standard 50 (modified by start point) of 90% of the skills, then it gets complicated, and I'd have to know the exact skill ratio to run the calculations.