I'd suggest you use the bag drop.
When you finish, your bag will be right there, for collection, and you can put fresh clothes on.
If your husband has difficulty getting to the finish (as well he might, the underground system is a complete nightmare on marathon day), then you won't be hanging around getting cold waiting for your stuff.
I'd also suggest arranging a meeting place a bit of a distance from the actual finish, too.
I've met my OH in Trafalgar square the last couple of times. It's much easier to move around there, not nearly so crowded. The area set aside for meeting up with people was completely impossible to move in.
Edited: 26/03/2012 at 15:45