Yes it's a fresh install (though not the first time ever on this machine) and yes I did try defraging & verifying the cache...it helped a little but not much. It's still pretty noticeable.
I'm a bit surprised this is the first time I've encountered this problem. In the past this machine has coped with HL2 & the episodes, Portal 1&2, L4D 1&2 and TF2 without so much as a glitch. The only thing I can think of that's changed is that I've probably upgraded the GPU drives a few times. Oh well, I'll just chug along and see if matters improve on their own.
In other news Black Mesa has been greenlit on Steam.
No clue if it'll make it on before friday. I'd be surprised if it does but I think I'll wait for Steam regardless...I mean I'm only in Ravenholm and have a long ways to go yet.