Re: dsl 401
The original speaker is a Celestion GT-100. Not a bad speaker for the amp. I upgraded it to a Vintage 30. It wasn't night and day, but it did make a difference, slightly more bass. A GH30 is supposed to be a little better for an open back cab like the DSL401, giving it more bass.
Avatar speakers is a great place to check out. If you're going for 2 speakers, a Vintage 30 and GH30 is supposed to be a good combination