Yes, you'll get the speeds you are getting right now, but on Tmo's prepaid $50 you'll only get that speed for 500MB. After 500MB you'll get throttled down to 2G speeds for the remainder of your cycle. Somebody like you who lives in such a strong Tmo coverage area should consider Solavei which is owned by Tmo and uses Tmo towers. For $49 you'll get 4GB of hspa+ (that is what you are getting now from Tmo), and unlimited talk and text. After 4GB you get throttled down to 2G speeds. I think it is really a no brainer for anybody to go with Solavei who might be considering Tmo's $50, $60, or $70 plas. I'm not with Solavei myself because I don't need the minutes and Tmo's coverage in my home is really bad.
Voice over data has worked only so-so for me. I don't have much tolerance when the connection isn't good even if it is only 1 out of 10 calls. Some people manage fine on it and it works great over wifi, but I just got too fed with it. The wireless speeds you get seem to be very strong. If you could consistently maintain those voice over data would probably work for you, but I don't think I've seen one post where somebody said they could use voice over data while driving in a car.