We sell a lot of low-stretch rope. 10.5mm or 11mm are standard, and most companies treat it as a consumable, so they go through a lot and generally buy mainly on price. The manufacturers know this and compete to be the cheapest, but customers quickly sniff out a rope that is less durable. Over the last decade Beal Contract and English Braids Tutus, both in 10.5mm, have been the biggest sellers. If they want a 'better' rope we sell them Beal Industrie although we only stock 11mm. Generous discounts to any walk in customers but postage costs aren't cheap.
I think all these are a bit thick for an ab rope and I'd go for 10mm or 9mm. If you have a belay device suited to 8 or 8.5mm ropes it may be difficult to use with a stiff 11mm - I had to carry a second device for a while when I was using Reversinos. Now I have a Pivot and a thinner ab rope. 9mm can be a bit terrifying on a big intimidating ab like you get in the Barra Isles, but like 8mm lead lines you get used to it.
I'm not convinced you need 100m and have always got away with less. Originally I got full 200m a reel very cheap and split into 3, they are generally a bit over length so plus stretch, minus knot, you get 70m+ which is plenty for Gogarth in my experience. I think on Pabbay we had a 90m 9mm which was long enough for the biggest abs although there wasn't loads to equalise anchors - you can always take have a separate 15m length for the rare times it's needed.
In the small print, most manufacters suggest 'conditioning' the rope by washing and drying it, just in water. This shrinks the sheath onto the core and washes out some of the lubricants used in weaving. You end up with a much stiffer rope without the supple new feel but in theory it should last longer.
As Lopez says, beware uncoiling rope that has been wound on a drum or reel. You may never get it properly untwisted. It has to come off like sellotape, which isn't easy if they've removed the drum it was wound on.
