This is what I've come up with, so far.
[hr][/hr]
Fiona's Mount of Awesomeness.
Spell Effect: ReTe(An)
This effect animates the statue and allows it to act as a real pegasus would. Base would be Level 3 ("Control or move dirt in a very unnatural fashion"), +2 magnitudes for "metal or gemstones," R: Personal (since the enchantment is affecting the item itself), D: Moon (+3, because I don't want to have to worry about landing at sunrise/sunset if I don't have to), T: Individual, +2 for size*, for a final effect level of 30. However, that would be just enough to give it Warping every time it's used (although Warping a metal pegasus could be awesome in its own way), so let's drop the Duration to Sun, for a final Spell Level of 25.
The item itself is steel (base metal, 5 base points), and at least Huge+1 (Multiplier x6), for a vis cost to open of 30 pawns.
The Spell Effect is usable twice a day (+1), for a final Effect Level of 26. We could make it constant by adding an Environmental Trigger (+3), to raise the Effect Level to 29, which would still cost 3 pawns. Or we could make it usable only by Fiona or by current members of Mons Electi (and their apprentices), which would also be a +3.
How does this look, so far?
[hr][/hr]
*Medieval warhorses weighed 1500-2000 pounds. I was unable to find anything showing how dense horseflesh was, but the human body is 1.01 g/cm[sup]3[/sup]. So, assuming that a horse has the same density as a human, and putting Aragorn in the middle of the weight range (1,750 pounds), that gives us 793,786.6475 grams, or a volume of 785,927.3738 cm[sup]3[/sup]/27.7547632730418 cubic feet. A pace is three feet, so that puts the total volume of the horse at a cubic pace, not including the wings. The base Individual for Terram (base metals) is one cubic feet. Two magnitudes would be 100 cubic feet, which would more than allow for the wings.