Which challenge? Run or Cycle?

My faithful Dawes Galaxy at Silverstone

I have in mind a challenge for next year.  Saying that is the easy bit, making my mind up is the difficult part.  I want a challenge, perhaps a running challenge - which I'll really enjoy - or a long distance cycling challenge.  Perhaps a tour or an Audax event.  Could even use one to train for the other.

So I need some suggestions.  I've looked at the Deloitte Ride Across Britain event http://www.rideacrossbritain.com/ and it looks tempting but I'm not sure I can hack 110 miles a day. What is even more challenging about this JOGLE (aka John O'Groats to Lands End) ride is that it would appear to be riding into the prevailing wind.  Surely LEJOG is kinder? Perhaps a lighter bike would help?  Then there's the good ol' CTC holidays http://www.cyclingholidays.org/.  Near my office is a branch of Cotswold camping and a while back I took a look at their range of single tents.  Some were really impreesively light and compact (is this what they refer to as credit card touring?).

The motivation for this falls into three camps:

1. Staying in good shape and improving my fitness
2. Having the satisfaction of pushing myself; an adventure, something new
3. Not having too many regrets when I'm a grumpy old man

Now it's October 2010 it's not too early to start training and planning.  Time scale to aim for is probably last week of July 2011 when Rachel and the girls are camping with friends.

I like the idea of a new bike.  Fantastic as my c1985 Dawes Galaxy is, I fancy getting something updated.  So what's so bad about the Dawes, apart from a few bits of rust appearing?  The gears are so awful I tend to heave myself up a short hill rather than change gear.  The imperial 27" tyres are increasingly hard to find.

I paid a visit to SJS Cycles to see their Thorn bikes http://www.sjscycles.co.uk/- particularly their Club Tour and their Audax bike http://www.thorncycles.co.uk/models.html.  I've also been interested in Evans Cycles when we pop into Milton Keynes as they always have a good range of fast looking bike in stock http://www.evanscycles.com/.

So, what's it to be?  Aim for an endurance event or ride?  Aim for a marathon?