Since I'd read _Silence of the Lambs_, it wasn't as scary on-screen

That's one case where I'm really glad I didn't read the book first.

I note that it and _Seven_ are both police procedurals,

Well, yeah. Both SotL and Seven were multi-genre hybrids. It's just that over the years the gap between the police procedural and the slasher flick (or, at least, the rampage-of-serial-killer subgenre of the slasher flick) has so narrowed that there's very little to choose between the two, so I didn't think noting that would make my point as effectively as did the film noir/character drama observation.

and I seem to recall that they get some useful tension out of this crossing of genres?

That's what I mean by crossing genres with horror making the horror more effective, rather than diluting it. IMO, it's like the difference between putting salt on a sandwich, and having a salt sandwich.

I feel tension too much on screen to watch most things in the horror genre, and even some that aren't.

I recommend that you do not watch The Others, then.

*is curious* Does this not-liking-tension thing also apply to action movies?