After completing all the nodes in the original star map you are continuously harrassed invited to attempt "the Steel Path" which basically lets you do all the nodes again, but this time with super powered enemies (+100 level, armor, etc). Since I'm now Mastery Rank 18 (which is the same level as our guild hall in Neverwinter Online) I thought I'd give it a try - and promptly found myself overwhelmed.
Which is great, as it forces you to learn more about weapons and builds to actually handle the increased threat which now includes acolytes of the Stalker invading every five minutes or so. It's still early days but I've found a solution in the Xoris, the frisbee Nef Anyo gives you during the rather early "Deadlock Protocol" quest. Using a heavy build to capitalize on double explosions (because apparently warframe frisbees can explode AND still come back to you) I've Firewalker Loki'd my way through a few of these now, with a Scourge primary to corrode the ones that need some armor reduction before throwing the Xoris at them.
It's good that there are five steel path alerts that take place regularly too, increasing the odds of finding a squad to go with. What I've noticed though is that in all of them I'm the only one using non-prime / non-lich gear. Maybe that will be my thing, to try beat the steel path without any primes. They're a pain to collect / pay for anyway. We'll see how we go. In the meantime, my reward is the Xoris totally obliterates everything in most normal missions now which is pretty sweet. :)