I have the iAudio x5 60GB version and I love it. When I bought the original (x5 20gb) it was great and I had only one problem... I have a crapload of music! I originally only had like 5GB of music and I just kept adding and adding... and now I'm at 14.5GB of music alone today. So, I knew I'd be needing more space considering I still add more music AND I use it like a thumb drive for transfering programs and such with friends and other people who might need helping cleaning up their computer (yay spybot and adaware).
So, I found myself in a bind. I could get the x5L 30gb, or the x5 60gb. Obviously I went with the 60gb because I knew I'd continue to add music; plus, now I have extra space to store more pics, programs, files, ect... and I constantly charge it when not being used in my car for music so the 15hrs is plenty (plus I own the car charger but hardly ever use it unless I am on the road for an extended period of time).
In your case, I'd get the x5L 30gb. It has 10gb less than the Gigabeat, the 35hrs continuous play, and a lot more features. I don't think you'll miss 10gb that much... plus 30gb is A LOT of music. I mean, I have about 15GB and that consists of 91 artists, 301 albums, and 3,390 songs... that's like 180+ hours of music with half the space the 30gb version will give you and 35hrs to start listening to all of it
$289.99 for the iAudio x5L 30GB
Your 40GB Gigabeat is $259.99 at NewEgg... so what's $30 for 10gb less space (that you probably won't use), WAY longer playback, and excellent features?