I've seen a couple of estimates of FM pace - though neither based on HM pace - and not necessarily applicable to someone with your relative strengths.
http://indoorsportservices.co.uk/traini ... thon_intro
says to take the difference between 5k pace and 10k pace, add that to your 10k pace to get your HM pace and add double it to get your FM pace.
Excuse me if my maths are wrong but looking at your signature you appear to have a pace of:
- 1:42.6 for 5k
- 1:48.6 for 10k
- 1:50.4 for HM
So you've already proved that link may not apply to you by having a much smaller gap between 10k and HM pace than between 5k and 10k pace (but if you did apply their formula you'd be looking at 2:00.6 - about what you've suggested)
The downloadable guide at http://indoorsportservices.co.uk/training/marathon
says '60-70% of 2000 m power in watts – closer to 65% or slightly below for the majority' and 65% based on your 2k pace would be a fairly brisk 1:52.4!
Applying the first of those approaches to my times would give an HM pace of 2:03.7 and a FM pace of 2:07.8 (scary!), and the second an HM pace of 2:08.7 (still scary!). Having said that, the first link is also based on a 24 week training program of either 80k or 110k a week - way way more than I currently do. Certainly expect my first FM to be in the '42,195 across a few intervals' type.