Sorry, Mickeg, I realise I wasn't clear enough in my first post, mistakenly assuming that anyone interested in this thread would be familiar with the Audax. It uses sidepull brakes.
I've replaced the original calipers with R650s which helps a bit, and have some SwissStop blocks which I've yet to fit....
I think the Thorn ST 700 fork fit the Mercury so presumably it can be used with the Audax?
Dave Whittle confirms that the ST700 fork can be used with the Audax, so I now have several options to reduce the effort needed for good front braking.
In ascending order of price and, I think, effectiveness:
1. Keep the existing dual-pivot side pull calipers and swap the STIs for regular brake levers and DT shifters
2. Keep the STIs but get a centre pull brake, which is supposed to need less effort
3. Use regular brake levers and DT shifters with a centre pull
4. Keep the STIs but swap fork to ST700 and use mini V. This fork looks less comfortable than my current fork
5. Keep the STIs but swap fork to more comfortable Thorn MER853VC and use mini V
Regarding points 4 and 5, my current, original Audax forks are very comfortable and have bosses for a lightly loaded carrier. I don't use front panniers but the bosses are very handy for mounting a battery light (I like to use a bar bag). The ST700 fork also has carrier bosses but is rated for a higher load (15Kg rather than 5Kg) so I assume it will be less comfortable. The MER853VC would be the most comfy of all but, quite apart from their price, have no other bosses than the brake ones so mounting a battery light safely might be difficult. You can get brackets that fit the fork crown like
these but I'm not sure I'd trust them. The light would only be for emergencies so it's not worth getting a hub dynamo.