In terms of general fitness for distance running, all other things being the same, race distance and past performances not taken into account and not that important.
Would it be more beneficial to run a 10k's worth of T pace work (meaning intervals, reps, single runs, etc.) twice a week or one day's work of 20k at T pace (being the same as it's 10k counterpart. i.e. comparing intervals to intervals and not single runs to intervals or vice versa)?
Does the larger volume of work at one time offset the added frequency of work in the week?
Is there any difference at all?