Dartcrafts lumberjack axes. I tried once with Axe of the stream, it caused so much lag that I couldn't stop it and it broke the axe. The lumberjack axe just cuts down everything above some 10-20 blocks up. Still it was too much work with the crown and I set it on fire with a wrath igniterIt would (wood?) be interesting to see some stats... How many blocks of Bark, Redwood and Redwood Root are contained in 1 13-block diameter Redwood that is 243 blocks high (I actually had one this big) and maybe how many saplings you could get.
I'd probably want to spawn myself a jetpack and a very powerful axe or 5, and a metric ton of the biggest storage available as well as 81 saplings to grow one 13-blocks wide.
[Edit] I wonder if it would be easier to use Turtles?
You could use a turtle, but that popular mining program for them wont work over a certain level(128 I think). Might be easier to try a quarry with some angel blocks.