After bleating on elsewhere on LB about cold fingers and having these Acerbis handguards fitted on my Honda Hornet 600 (http://www.ams4ktm.co.uk/shop.php?product_id=3466) I thought I should at least report back my findings:
This morning I did a 34 mile trip which took 50 minutes and one I do very often (Heathfield in East Sussex to Oxted in Surrey). Although my average speed works out at about 41mph there are whole sections of 60mph riding on a mix of A and B roads as well as much slower in-town sections.
It was -1 when I left and 0 degrees when I arrived but I went across Ashdown Forest where you can feel the temperature dip dramatically for about 15 minutes riding. In these sort of temperatures I’d normally have to stop at least once to regain feeling in my fingers and, when I arrive, I normally go through 10 minutes of absolute agony whilst blood returns to my finger tips.
Today I did the entire journey in one and can actually feel the warmth of my heated grips at speeds below 40mph whereas previously I’d be convincing myself that they weren’t actually working atall. I still had cold finger tips but the pain was manageable.
Conclusion: I’m really pleased and, for the daily mileage I do, they help enormously. If I did longer/faster rides I think I would definitely look at heated gloves as there is still pain involved, just not the writhing/screaming kind anymore! 
