In reply to bogpetre:
If you're out there for a month, you should get some decent conditions at that time of year but not every day of course. There's always a chance of a really wet summer like two years ago when you can't get much done; or else a really hot spell like last year when the glaciers and bergschrunds start to really open up, stuff doesn't refreeze overnight and some rock routes become dangerous due to rockfall but even then you can still get stuff done with careful route selection. However the average mid July to mid August season is going to (1) be very busy and (2) have variable weather from very good to very poor, but on the whole you should be able to get some good stuff done over a month unless you're really unlucky. Of the routes you mention, all may well be doable, apart from the Whymper which I think is more of an early season route these days. Also bear in mind that the weather and conditions can be much better down south in the Ecrins or out east in the Valais when it's crap in Cham.