I did flax all the way to 50. It really depends on how many leves you got available. Linen Wedge Caps of Gathering are extremely easy to make and the mats are cheap. The only thing that might get a little annoying is the constant runs to the Observatorium to turn in the leves, however that run is also granting you bonus experience. Since you're only turning in 1 hat a time, you save a lot of money on shards (not to mention time), and you get to avoid wool and felt. Just make sure you have like 50-60 leves available... or you can do Linen Hats instead.