I finally had some luck last night that's really boosted me, I dropped an awakened greater multiple projectiles gem and sold it for 10ex. I was then able to corrupt one of the Enlighten gems I'd levelled up to level 4, I sold that for 4 ex and the other 5 for about 1.5ex total. I then sold all of my fusing, jewellers and ancient orbs (harbinger farming has been great on the side) and was sat at around 20ex total.
I scoured trade and managed to find a pretty beasty bow, I sniped it for 12ex when it seems like the going rate was much higher:
+1 to all socketed gems
+1 to all intelligence gems
+1 to all strength gems
Crafted:
+2 to all support gems
38% more Chaos DOT multi
It puts my Bane to level 29 and I can still push it to 30 as well once I get an Empower level 4. Damage literally tripled just like that.
I then managed to get a Divergent Berserk gem of which there only seem to be a couple on the market at a time, paid a little over the odds at 7ex to just get one whilst it was available, that's given even more damage and survivability. It feels pretty safe so far, I've only died once in the last few days and that was when I got disconnected. Mana/HP recovery with my permanently on flask is just over 2.5k a second, I now just need to squeeze a few more levels out and buy some more optimised cluster jewels to push it further, I should be able to get it to around 5k per second with the right set up.