To me, the concept of using Fate points to confer the temporary powers seems to tarnish the magical nature of thaumaturgy. I like the taken out concept better, personally, with additional shifts to define the power (so 4 shifts can provide a 4 shift effect, 6 shifts for a 6 shift effect and so on). I'm thinking of house ruling it like this:
To give someone with an Endurance of 4 (giving 4 stress boxes) supernatural strength for half an hour, taken out is 5 total shifts, plus 4 shifts for the effect, plus 7 shifts for the power to last one half hour.
5+4+7=16
Now to adjudicate how that affects the character physically after the spell wears off, I would say they are struck with a physical attack of the power plus the time, minus their Endurance and given consequences appropriate to the situation
So 4+7-4 = a 7 shift physical effect that bypasses any toughness powers they may have and armor they may be wearing. Lord help them if they caught other Consequences, because that would hurt.
Obviously it's a house rule, but does that sound fair?