Here 3G zte mf180 USB modem connects at 3Mbps, Windows Task Manager, Network Status, etc...
Connection rate and data rate are different...
Very much so, as I recall my connection rate reported by Windows was something crazy high like 8 or 10 MB/s even though the actual speed of the actual connection was tons slower.
BTW, my experience with anything ZTE has been uniformly negative - IMO ZTE builds JUNK and should be ignored.
This is actualy the norm for anything resembling a serial modem, back in the days when dial-up was common most modems had a connection to the computer that was a lot faster then the actual modem connection speed (mostly because of data compression being common in 9600 baud and later modems).
As far as your 2GB cap goes - I was on one of the Virgin Mobile "Unlimited" connections - my SPEED got capped at 5GB downloaded after about the first year when they unilaterally changed the plan to a semi-capped plan, but the speed cap was pretty close to the NORMAL speed I saw and was pretty much unnoticeable as a result.
Unfortunately, unlimited seems to be pretty much dead on cellular connections - even that old Virgin plan got phased out and only folks that already had it and kept it current could still use it.
And yes, I'm aware that it varies - not just by country, but sometimes by area IN a country and always by vendor.