At this point in time you can only get a max of 30 Agony Resistance (AR) which is insufficient for surviving the Agony that hits you when fighting the Jade Maw boss. I can only imagine this getting worse as you approach Fractal of the Mists levels 50-60 where AR won't help at all.
What strategies and tactics are there for getting past level 40 difficulty?
Best Answer
It is very hard, but apparanetly it is possible, as you can check in the following screenshot (link here):
According to the picture owner, the maximum level is 80, you can get pass 80, but if you leave it, it will reset to 80.
At level 40, Agony does 72% HP/Sec with no resistance. At level 50, 60, 70, and 80, agony continues to deal 72% HP/Sec with no resistance. The exception to this is Jade Maw. At level 50 and above, Jade Maw's agony deals 1172% HP/sec (source). So the only boss that seems to be really hard in 40+ levels is Jade Maw, as the others you can find some ways to avoid Agony.
According to this guide, there are a few tricks you can use to survive.
In the other bosses case, I would recommend the reading of this guide and its useful comments