[killernoodle]

I dont think you should worry about 2-4C, and the spiral isnt known for extreme performance. I also dont konw what kind of air you are pushing through the bigger heatercore.

You can tighten a block pretty tight against the core, Dont let it go loose, especiall if you are putting thick tubing on it. One of the worst things you can do temp wise is put a lot of torque on the waterblock and allowing it to get crooked on the core. Not to mention the risk of cracking it.