Convoluted counterflow chiller internal tubing size

I've been looking at a few of the commercially available convoluted counterflow chillers and I'm wondering if anyone has experience with them. The ones from Morebeer have 1/2 inch wort tubing and the ones from Midwest Brew Supply have 3/8 inch wort tubing. Both are 12 feet long with a hard copper outer tube. Has anybody used these? Is there a significant performance difference between the tubing sizes? I'm planning on recirculating the wort back to the pot using a pump until I get to lager temps, so it doesn't have to hit the temp on the first pass. I will use it for mostly 5 gallon batches but occasionally for 10-15 gallons. I plan to use a pre-chiller for the water. Any advice? Thanks.