When my DV was shafted it didn't really sound any different to when it wasn't apart from the lack of hiss on lift off. But the lack of power delivery, at the rev you describe pretty much mirrors what mine felt like when it was knackered mate.
If I remember correctly yours is an 05 model isn't it? Mine is too and with 50k on the clock it had completely destroyed the original DV, and I mean completely.
For £55 I'd just replace it anyway to be sure and a local garage will fit it pretty cheap if your not able to swap them yourself.
