I was thinking of asking a similar question regarding loading Santa's latest gift, my new Stella SW18000HG. The three criteria that concerned me were the capacity, having enough even tension, and keeping out twist. Whatever I do not want the braid cutting into soft layers underneath if I can help it, and I guess good tension will give me as much line as I could put on the reel.
As it turned out I got just over 300m of PE#8 YGK ultra on it, loaded without twist, and a nice even tension.
I achieved this by letting the braid come off the retail spool without tension, in the usual fashion so that it counteracts the twist put in by the bail, and then threaded the braid through a Tiagra 30 (held down on a table by a friend)taking the braid round the spool a dozen or so times and then off the Tiagra spool and threaded through the rod guides and onto the Stella spool, set the drag on the Tiagra to apply enough tension to the braid coming off the Tiagra spool and onto the Stella, and wind away till the Stella was loaded. This seemed to work really well as the spooled braid is really solid on the Stella.
I know its a bit late to ask for my new baby, but what do you guys think would be the ideal tension to set the drag on the Tiagra for for PE8 or a fighting drag on the Stella set at say 15kg ?