The 7.10 rod will make the lightest rotating assembly, so I would go that way. Some will say the shorter rod will make more torque, but I have read differently, from some very knowledgeable people. Besides taking stress off the main caps, the lighter 7.10 deal will have a little less side thrust on the cylinder walls, and it makes sense to me to build a stock block motor for the least stress possible. I split a cylinder in a 400 block years ago that checked OK before machining, so I like to err on the safe side.