hi, welcome to the forum, every test I read and every experience I made make me conclude the 3/8 tubing give the same results as the 1/2 , for the question about slim rad, well first tell us what case you are using as you can't expect as the smae results with a thin rad than a thick one, the surface is not the same. You will not run a CPU, a board and 2 GPU with a 280 , I just say in case. So we comeback to square 1, what is your case ?