Doc,
I'm experiencing the same issue as you. I've been in email conversation with the community manager at Urban Games and they are certainly interested in the issue. They took some of testing and observations and have now passed it to the programmers to look into. If you haven't already done so, I'd suggest contacting them at [email protected] as well.
From my perspective, it doesn't seem to be a CPU horsepower issue as much as the "logic" the devs have put into the game's decision-making process. My suspicion, and it is just that, is that went they made the new multi-thread update, their coding for the In-order/out-of-order threads and branch prediction may not be as efficient as intended. I have a dual 8180 Xeon workstation, that doesn't even notice this issue. but that processor has deep IO/OoO branch correcting instruction sets.
My main gaming system, while older, ran the game as smooth as silk, and no real issues. Now it's almost unplayable. It took me 20+minutes to make a simple double-track to double-track interchange on absolutely flat and even ground.
When I need to bulldoze in a city, attempting to eliminate a street with any interconnects with other streets and or rail and easily lag out for a minute or more.
This is my go-to game to relax and take my mind off things. I hope they get it fixed.