Since this seems to be a dual purpose truck, you will have to decide which is more important. Engine speed on the highway or engine speed at the 1/8. Check out
http://www.wallaceracing.com/Calculators.htm and there will be a calculator to figure out your rpm questions.
The converter question is somewhat the same issue. Driveability or e.t. If you get to high of a stall speed you are going to hate it on the street. You will run a higher stall on the track only. Both ways probably 3000-3500 or so but not knowing anything other than size of your engine it's really only a WAG at it though.
Curtis