Thanks roastman

Rick - not sure what you mean by based on that thread, but what I find with the 400D is that I have a lot of trouble focusing and getting sharp images on moving objects in low light conditions and I get a lot of noise if I crank the ISO. I basically don't use the 70-300 kit lens because it's never really seemed to focus well which is why I brought the L lens as a replacement. The 18-55 used to be ok but it has started to play up sometimes too. I was going to get a replacement for that ages ago and had some helpful suggestions on here but couldn't get the OH to agree (no longer an issue as he's not around now).

Of course, I could just get a new lens or two for the 400D but if I spend a decent amount of money on crop lens and then decide to go full frame I'll lose some money on that.

Open to suggestions