Shaun, here's a bit of advice from someone who probably isn't qualified to advise you as although I understand some of the theory I've never been able to do high mileage training because I pick up too many injuries.

My answer is that it's hard to answer your question on the basis of the info you've given so far.... depends on what volume of training you've been doing over the last few years and how fast you've built up the mileage. I seem to remember Ian Holmes saying back in about '96 that he was having an easy week of just 60-65miles after completing the british champs and this stuck in my mind as I was thinking "but my biggest training week ever was only 50 miles".

There's lots of info around on relative volume of training in the weeks of a training cycle - ie what %of a month's training time you spend in each of the weeks - but as I'm at work (!) I don't have anything to hand. The intensity also makes a difference: if your hard weeks include eg 3 hard sessions and your easy one includes only 1 then you're getting a relative rest in the easy week even if the mileage isn't much less.

To some extent you'll find out by listening to your body and by trial and error: eg why not have a properly easy week (ie 20-25 miles) and see how you feel afterwards?

One thing I would be really conscious of is what your legs are telling you - if there's any sign of a niggling injury then ease off, as significant increases in volume can easily lead to injury, stress fracture etc. And if you have a hard, stressful period at work you may want simply to enjoy running in the hills rather than hammering it.