How much does knife thickness matter? I was looking to buy myself a chef's knife, and was interested in either the Richardson Sheffield V Sabatier range, or their Sabatier Trompette range. Now, the latter is a bit cheaper, and the only difference I can see between the two is that one seems slightly thicker than the other. Neither is flimsy, but the V Sabatier's blade is about a millimeter thicker.

I am looking for a good quality knife that will last me, but I don't want to spend more money than is necessary. Is the extra thickness worth a ~£10 premium?
Extra thickness can be useful, but it can be quite annoying too.  We have some real knife experts here who will probably go into more detail, but as a kitchen amateur (using the sort of grade knife you're looking at) I tend to use a thinner knife for most things.  Much of what you use a knife for is slicing, and a thick knife adds nothing there. It can even mean that slices break or fall away before you're ready.

A thick, heavy knife is useful for various  things, like fine chopping at one extreme, or getting through a butternut squash at the other, but I wouldn't want to only have thick knives (my thickest knives are tucked away in the second knife block).