what size pickup and lines for a small block...

Im replacing the entire fuel system in the 70 dart by necessity.....

my question is that I see that I can get a 5/16" or a 3/8" pickup in the tank. I can also order the lines in 5/16" or 3/8". Currently the car will be a mildly warmed 318 with plans of one day running a big block or a 408 stroker from a 360 magnum I have.

Should I order the 3/8" parts? Is the 5/16" stuff enough to keep up with more than a stock small block?

If I've got to buy it anyways.... I might as well only buy it once ya know. Thanks