Boromir and his search for Rivendell

[Pervinca Took]

You don't gallop a horse for thirty miles- at least not a real-world one. Just the mile-long sprint to the ford would have blown him!

G in fact tells Frodo that "Elrond's folk met [Aragorn and Glorfindel], carrying you slowly towards Rivendell."

Yes, but they couldn't have got that far before the aid came. If there were still thirty miles to go, the Elves that met them must have met them pretty soon and had fairly efficient transport. I'm not sure what time of day the flight to the Ford happened, but Frodo was brought to Rivendell on the night of that day, I think it says. A thirty-mile canter, perhaps?

I too had always had the impression that it was only a couple of miles or so. However, the Tale of Years says that, on the way back, they leave Rivendell on 5th October and cross the Ford of Bruinen on the 6th.