Ok, so today I finally completed phase one of my "Dream Setup" Plan. I have a 5150 II that I got used for £550 about 3 weeks ago, and today I got my new cab for £450. It is a custom made cab by Matamp and features 4 Celestion Hot 100 speakers running at 16 Ohms. Now, before I got this cab I was using my old Line 6 cab which I am selling as soon as possible along with the head. That cab was runing at 8 Ohms. My normal volume was usually about 3 or 4 with the Line 6 cab, but today I noticed that with ther new cab, that volume is equivalent to about 2. This seems strange to me as I was quite sure impedance didnt affect volume? Am I mistaken or is something more sinister afoot?

Also does it make a difference volume-wise if I only use one speaker cable as opposed to using both inputs on the cab and on the head?