Last time I played SCL6, pretty good, but not optimal play had me in t5. If things haven’t changed (and that’s a big if, because that was like the second event with a required 5*), as long as you’re doing 7 clears, you should be able to get t50 even if you’re not doing them optimally.
T50 in SCL6 gets you about half the HP that SCL7 does. But if you don’t have the 5*, it’s basically a choice between half the HP in 6, or none of it in 7, because you’re not placing high enough for it without that node.