Swiftness Boots!
I suspect that if item-based run-speed comes into GW2, it will appear as a utility infusion. I know I’d love to have a 25% speed infusion. More would be too much and less would mean I wouldn’t buy it, since signets already do 25% for most classes.
BTW, mesmer works wonderfully with centaur runes. You can have nearly 100% swiftness by combing that with the healing meditation.