340 is a performance engine, there are no other versions of it. 70 and 71 are the best years for them, because of the internal forged components; IE crank, rods, pistons.
They were in a lot of low buck light cars, they could easly handle higher revs than there bigger high cube heavy brothers. Lots of advantages as Harkonnen said, not hitting the high dollar mark yet thankfully.
383 has the torque at low end, 340 well be the high horse power rever. They're evenly match up, not sure about what is the difference in weight. 100lb 200lbs?