Okay, opinions are worth what you paid for them, so here is mine. I would say go with the 380 for the following reasons:
First, you can get a 380 for about half what you would pay for a 420 of the same vintage. That's a lot of money
that you could use to extend your time out cruising.
Second, the vertical or bridge clearance on the 420 is 68 feet. Many of the bridges on the ICW
are 65 feet. The 380 is a much more reasonable 57 feet. This may not impact your plans too much, but it may have an impact on your ability to resell when your journey is done.
There's not much difference in draft
between the 380 and the 420, so that is a wash.
Lastly, if you can be comfortable in the smaller boat, that's the one you should go with. You'll save money
and it's just that much less boat to maintain.
Full disclosure, I have a 37 foot boat and I'm constantly on yachtworld drooling over 44 footers. However, in the end I always come around to the realization that my boat is perfect for me. Hopefully you will be happy with whatever decision you make.