Luke I have had a similar issue with my stella 10000 and after a lot of mucking around I went and brought a JM 1600 spool.
Stripped it down yesterday and easily saw why they get the extra drag they claim.
A set of 6 carbontex drags in the main stack and a further 3 stacked under the spool
The engineering is impressive to say the least.
Then just replaced the standard washers in the stock spool and will use this with 50lb braid
One other thing to check is the Bail arm roller bearing as I spotted mine had corroded badly and needed replacing.