Better Midweek Workout: Tempo or Goal MP run?

All things being equal what is a better midweek workout:

Eight to 10 miles at goal MP, or

Four to six miles at tempo (~HM) pace?

I know some don't believe the marathon pace run is fast enough to solicit the physiologic (is that a word?) gains but if that were true I must be doing something wrong. I am very tired after eight marathon paced miles midweek let alone 10. Thoughts?

Honestly, I hate to pick one over the other without the overall training context.

With the caveat that I don't do GMP runs, I'd say the tempo run is better, but even that should be in moderation.

MP runs typically take a lot out of me - even just 5-8 miles - until I start including tempo runs. Then 10 miles @ MP is cake. When peaking, I save the MP miles for a fast-finish long run and put the tempo miles midweek. In overall training, usually a little of both.

I do mid week tempo up to 7 miles. Every few weeks I add MP miles to my long runs - like in Pfitz. schedule.
Mp long runs are good psychologically. as my training progresses, the tempo runs seem to get easier so I know they are helping build my faster running endurance.

Based on the way Dave, Chris and I performed in Chicago with an emphasis on longer mid week "tempo" runs that were really closer to MP, I'd have to say the tempo is a more effective workout. I've felt much more fit doing those and recover a bit quicker as well since it's less "hard" mileage.

I would go with the tempo run...based on an easier recovery for longer weekend miles.

Tempo for me no doubt.

Or you can rotate.