I made some changes that may or may not do a difference, let me know
Ok I will give you my experience after this patch.
Got the Quest for doing the Queen Matriarch, the one where you have to have 10 myrmidex warriors, 10 Drones and 20 Larvae. Went to the Dragon Turtle spawn first to get the Larvae and Drones, no problem, running good - no lag to notice at all, went back to area by Brit camp to get the Warriors, got them no problem - no lag to notice at all. Very pleasant, moving fast, was cautiously enjoying the newfound movement, memory use about 300MB.
Went back and turned in quest and got another of the same. Again to Dragon turtle spawn, now some lag, not bad but some and swiftly grew more severe when I had a multitude of them around me, finished those larvae and drones and by the end lag was bad, not terrible but bad. Went back to Brit camp and to area to kill the 10 Warriors, lag not bad to start for running until you got 2 or 3 around you, drones, larvae, scorpions, warriors and it rapidly became horrible with probably one second lag between each step that I would try to move. After that it didn't seem to matter how many were around me, lag, rubber banding, damage numbers rolling in hoards slowly up the screen, horrible. Checked the memory, was around 500MB, actually less than average from this same time before the patch.
Managed to finish, and went back and turned in quest, the strange thing or perhaps is a clue, when you get away from the monsters I am able to move at normal speed almost immediately. And this is true and has been true of all encounters with the larger monsters now after the patch and before the patch, when you finish the major task, the lag is not even noticeable and no lag on normal running at all.
I didn't really check but I would estimate time for doing these 2 quests was between 20 and 30 minutes. Recalled back to house, checked memory, now at 300MB.
Don't know if this will be of help but perhaps you can replicate that if you try the same procedure.
FYI I run a Gigabyte Z97X Gaming Motherboard, i7-4790K Intel Processor, 16G Ripjaw RAM, Intel SSD, EVGA 960 4G memory video card, Internet connection 100/10 Fibre Optic. I have no lag issues with anything else on the computer except for these described instances in the game.
Thank you for your time and help.