a 47min 10k should get you closer to a 4hr marathon with some application. my 10K PB is just over 45mins and I have a 1:45 1/2 and a sub-4 marathon (by 8 secs but who cares?) - and I was over 50 for all of them
so some speed or tempo work can help you get faster - just don't overdo either and build up.
I tend to run on feel these days, not HR as I've given up PB hunting - saves worrying what my HR is doing and my experience tells me how I'm feeling
get rid of the virus first and then start applying yourself. google FIRST run training - it's speed based training regime which uses the 10k time as the baseline. but be careful not to go too hard on the speed sessions - that can lead to injury as I found out
Edited: 26/11/2012 at 17:23