Hey Susie, I think alot of the speed work is based on your 5k and 10k running pace. Do you know what yours is ? How far are you running for your tempo runs ?
Recently I did some intervals of 1 mile warm up, 1/2 mile at 5k pace, 1/4 recovery x 3, cool down.
I am training for a half marathon in September, I hope to run it at at 9/ 9,30 min mile pace. The training plan I've been looking at does suggest running some 10 mile runs at race pace to see how it goes. And also run 13 miles, with at least half of that at race pace. Your half marathon pace should be faster than your marathon pace. I'm guessing you'll want to run about 9.45min miles if you want to beat your 2.09 pb. So I guess maybe run 10.30min miles for part of your long runs.
I hope all that made sense !