Over heating questions
Change you thermostat to a 180. That 160 stat is doing nothing for you except shortening your engines overall life-span.
If you are hitting 210 (which isn't hot) while sitting in traffic on a 90+ degree day, that's just about normal.
What kind of fan do you have?
When, specifically is it getting in the 210ish range?
Do you have a fan shroud?
No, going to a 4 core would be pissing money down the toilet.
To long, didn't read version: Put in a 180 stat and keep driving, your car is fine.