Nick,
I was going to buy the 20XLc but on the advice of folks here I wanted to try things on first. Luckily, I had the opportunity to visit Sporty's in person and try on several headsets.
I did go with a Lighspeed, but I decided to blow the extra 40 bucks and get the Twenty 3G instead. It has somewhat larger earcups and I found it more comfortable because of that. I think it sticks out to the sides a hair less as well. The rest of the differences are quoted below.
I don't regret the purchase at all. I used them on my Gaston's/Texas trip this summer (MSN - 4.3 hours - 3M0 - 4.4 hours - EFD - 5.3 hours - SIK - 3.5 hours - MSN) and my head and ears still felt great. I've even used them for up to 8 hours at a time while driving, same deal.
To clarify the volume issue - The volume controls on the battery box control the aircraft volume ONLY, not the cell/music volume. So, you'll have to use the volume control on your iPod.