nice sessions going on, johnas, no wonder you didn't fancy that before work! I know you call a "session" a hard work out, so i've never done one pre a full day's work. Have done some utterly monster sessions at lunch before though, and come in wiped out 
Heading towards shorter distance biased work now. And after years presuming I was some kind of short distance specialist, i think the evidence and feel is screaming the opposite these days.
It does take getting back used to though.
Aim was 4x800s at 5.30,5.20,5.10,5.00 pace off full recovery.
I judged a full recovery as 2mins, although that could probably have been a minute longer.
800s came out 2.43,2.39,2.32,2.33
x2 + the 2secs to round it to a mile, that makes paces of 5.28,5.20,5.06,5.08
Not too bad then, but the 3rd one came out a bit too fast and probably disjointed the 4th one.
The wind was down the 200-300/500-600metre part of each rep, and although smashable for the first lap, became a bind for the 2nd lap. The wind disappeared down the back straight and felt like I was jet heeled in comparison!
Therefore,a decent enough session, doesn't hurt to sometimes not smash the target, it's all good training.