That's good stuff Rachel, that should get you used to running fast. Not that you'll be running your marathon at that pace, but it'll help your marathon pace feel easier, something you don't get if all your running is at the same pace. Variety and all that, eh?
It's a bit of a guess, but based on today's effort I'd suggest something around 8:30 for your run tomorrow. For anyone lurking, that's not a fixed pace aimed at achieving a 4 hour marathon: rather it's an individual thing, you should be running just beyond conversation pace, but not quite up to full 5k or 10k race pace.