Re: interval training at the cost of long runs?
I have only been running 7 months, and less weekly mileage, about 18-25 currently. I have found success by doing an easy 3-4 mile run, a tempo or interval run of 5 miles, another short easy run, then a 10 miler or 8 miles with hills at a good pace for my long run.
like you, I find it difficult to slow down, but feel that with limited miles I should try to do harder runs than someone running further. (Quite often I do only 3 runs in a week, for the lower total.)
Being 56 I find it takes me a bit longer than some to recover after a longer or faster run. I ran the Toronto Sporting Life 10k on Sunday in 51:50, but it is flat or slightly downhill all the way so perhaps adding 2 minutes would give a fair comparison.
My point is that I think what works best for each of us may be an individual thing, I do think more mileage would make me faster, and am planning to gradually increase with the goal of running a half marathon this fall.