Thank god.. I'm also similarly challenged.. but either way it's 6:36 or 6:40.. 10% of 6:00 is 0:36.. so 10% slower is 6:36.. or 6:00/9*10 = 6:40..
which in incidentally what I do most of my long runs at.. well 85-90%.. never worked it out by that just happens to be around 6:35-6:45 pace..
I like the idea of reps in the pace, but that's essentially the old Charlie Spedding session isn't it.. reps at marathon pace with recovery at ~ 1 min off that.. so I do 6 min/mile and 7 min mile recovery..