For those of you with dual core CPUs (2 cores) that are getting frame stutter / lag try the following, it might also help those of you with multicore systems who crash/freeze.
Disable Multicore rendering through cvar command
(Since we don't have it working in the advanced video options at the moment)
While in the PVKII Menu, open the console with ~
(if it doesn't open go to options, keyboard, advanced and then check "Enable developer console")
type mat_queue_mode 0 to turn multicore rendering off.
(mat_queue_mode -1 to turn it on which is default)
You can also add this to an autoexec.cfg
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Or you can follow the steps below, but it's much easier to do the above.
Try setting hl2.exe's affinity to one core only once pvkii is open, if you don't know how, read below:
(Make sure when you do this, you're not in a server already, you might cause reflective surfaces that use cubemaps to have a pink checkered look and then you'd have to restart the game)
Start PVK II, alt tab out of the game then ctrl+alt+delete and select task manager. (Or start, run, type task manager)
Go to the processes tab, scroll down the list to hl2.exe, right click on hl2.exe and select "set affinity"
After select affinity is selected a dialog box will appear with the two CPUs, uncheck one of them, click okay, close task manager.
You're done for now, maximize PVK II and try playing and see if it lags.
If this works, you'll have to do it each time you start the game.
Hopefully it should fix it for most of you.

Comments
I get FPS drops which did not happen in 2.2 and this fix does not work.
When there will be a hotfix so I can use mat_queue_mode 2 (Multicore)?
I also get it in the Vikings, and pirates area too. It seem to happen on the whole map.
1) Open Steam.
2) Select the Games Tab.
3) Navigate to Pirates, Vikings, and Knights II.
4)Select Properties.
5)A window should open, then select Set Launch Options.
6)A text box should open.
7)In that text box write "-high".
There you go, now pvk will automatically be set to the highest priority everytime it opens!
Join the Club
What is are your computer specs?
it pisses me off so much I tryed EVERYTHING.
WITH ME
its since the latest update....
please fix this:(
I get FPS drops which did not happen in 2.2 and this fix does not work.
I have this processor too, and the game freeze for ~0.5 secs. often..like at 1-1.5 minutes
http://dl.dropbox.com/u/11068560/ovju.jpg
i5 2500k
GTX 570
8 GB RAM
Windows 7