Yep, everything in a single continous loop.
You don't need to add another rad: you don't have the heatload to justify it. (i.e. you'd be wasting your money).
If you did add another rad, you'd set it up in parallel with the other rad, but only for those cases where the flow is so high, that you need the split to get as close to 1.5 gpm through each rad (point of "highest efficiency"): there's also no sense in dealing with the pressure drop of a rad above 1.5 gpm.
The delta T that you refer to otherwise is so small, that you may not even be able to measure it. I'll refer you to an article by a colleague of mine, which includes a formulae to calculate the temp difference, in and out of a waterblock:
http://www.nordichardware.com/articl...vattenkylning/