I got the Creative HS800 Fatal1ty Gaming Headset in October 2008 (according to my records on Amazon) and it's lasted me really well, the only reason I'm not buying a new one is because my friend put snow down my neck while I had it on and in my rage to attack him I broke my headset. Even now it works fine but's getting a bit wobbly.
Anyway, I like the sound quality, although I only have the onboard sound (sounds like the same as you) not a separate sound card. It might be that I have never appreciated the quality a £150 headset can provide you but honestly, I don't want to pay that much for a headset then accidentally wheel my chair over it (current one has survived that a couple of times). It's comfy to wear and I used to play guildwars for 8+ hours in a row with it on. My ears used to get a bit warm though.
I decided to just order another razer carcharias. Good sound, really comfortable, good mic, and I have experience with it