One helpful reply, thanks a lot wareya.

I'm going to keep this short(-ish). I've been playing for 900-ish hours, and I've spent quite a few of them as Spy. I used to be a fairly decent shot. Then I moved, and spent a year with crappy DSL that messed a lot with TF2, meaning I didn't play much during this time. No config changes helped, ISP couldn't do anything. I eventually wound up getting fed up and switching to cable. Since then, I've been playing for a week or two, and I'm noticing that, even if the connection is better, I still have a lot of trouble landing headshots with the Ambassador.

What happens is that I click on someone's head - normally you'd think that'd be it. It took a while before I realized that I have to aim higher than usual to get my headshot registered - then, sometimes, that doesn't work either, and I just miss. This also seems to be the case on still targets, so I don't think it's my (rustiness).

A lot of people are just saying "that's how Source is", and I would believe it - I'm fairly sure it didn't use to be like this, though! Is there anything I can do to fix the problem? I'm posting my config here, not that I think it'll do too much good, it's pretty standard (from Chris' configs)

cl_cmdrate 66
cl_interp 0
cl_interp_ratio 1
cl_lagcompensation 1
cl_pred_optimize 2
cl_smooth 0
cl_smoothtime 0.01
cl_updaterate 66
rate 60000

The usual suspects like interp and mouse sensitivity should be OK - tested interp around 15-30ms, mouse sensitivity is pretty low - 360 on my entire mouse pad.

Very grateful for any help. :)