I have a 405cx that I originally purchased for running. Aside from the battery draining overnight, which a firmware upgrade fixed, I've never had the issues with the 405cx that other people have had. I use it for biking, but the battery life isn't very good; I think mine only lasts 5.5/6 hours anymore.

What about the 310xt if you need a replacement and want something to wear on your wrist? It has up to 20 hours advertised battery life (comparable to the the Edge 500) and does everything the Edge does except it doesn't display temperature. If you use a heart rate strap with your 305 it should work with the 310xt, which means you'd only need the $200 model versus the $250 model that comes with the strap. Until August 31st Garmin is running a promo where you can trade in your old Garmin for a $50 rebate on a new Forerunner through their Girls Can Run program.