I've appreciated your comments about a climbing system.
here: Mast climbing
The next item is the actual line. I'm planning on getting 350' of line.
My first thought was 7/16 to 1/2 sta-set which is readily available and is rated up to 9,000 lbs.
NEW ENGLAND ROPES White Sta-Set Polyester Yacht Braid at West Marine
Then I saw this. Less than half the price, specially formulated for climbing.
Also I figure 12 braid will stuff in a bag with less chance of hockles.
Arbor-Plex 1/2” Rope
The line rating is 9,000 vs. 6,000 but I'm only 200 lb and I'm using a 4 to 1 purchase so the line will be loaded something above 50 lbs.
Hmmm. I'm gonna say this is all pretty wicked overkill. I was an arborist in a past life and am still a regular rock and ice climber. I have a lot of experience with ropework and you're already breaking the first rule. KISS.
You don't need 350' of rope and you should steer clear of any complicated blocking systems. You're just trying to get yourself up the mast.
Here's how I do it:
A) I use a halyard. No sense in hauling another rope up the mast.
B) Rock climbing harness with a petzl grigri on a locking biner attached to the belay loop as my hard attachment. There are other ways to do this that are more convenient for ascending, but the grigri has the advantage of being useful for descending without having to change gear.
C) Simple ascender with a long (48" or 72" I forget) runner on the rope above my grigri, not attached to me at all - I use a rock exotica rescuscender, but they don't make them any more. Anything will do though, including just a prussik or a tibloc.
D) 48" runner double girth hitched to the mast, on a biner to my harness.
Climbing is a simple procedure. stand up in the loop attached to the ascender, pull the slack through the grigri, sit down on the grigri, advance the ascender a couple feet and repeat. As you do it, you slide the runner girth hitched to the mast up to provide a backup (if you are worried about the halyard.
To descend, you just remove your ascender and rappel on the grigri.
Easy peasy, no need for 350' of rope.
I would be real hesitant to get involved in anything complicated. The only skilled ropework guys you ever see getting involved in complicated systems involving lots of rope and mechanical advantage systems are rescue guys and that's because they're dealing in such high loads.....
If you insist on buying rope, arborplex will do OK. It has a very soft jacket, which is fine in an arborist climbing system, but will get chewed up fast if you're using any toothed ascenders on it. (I'm still not 100% sure what you're planning). If you're gonna use any toothed stuff on it, go to your local climbing shop and tell them you need 10mm static line.