The modes in my room boost the LS50 down low.
You get a better idea of the extra extension by looking at what happens from 150 down to 60.
IMHO, the LS50 has issues even with a sub.
Here's a more carefully done comparison from my listening position with an 80Hz crossover to my servo sub. The sub has been EQed.
The dip just above the xover is because the LS50 starts rolling off at about 150Hz. The R300 (even with port plugged) does not.
So I would pick the R300 as it has a fuller range without a sub, and blends better with a sub.
I would pick the LS50 if you only listen to small scale music, your room has big bass boost, or for aesthetics.
But were I putting my money on the table (which I may be soon) I wouldn't get either.
I'd get the R3.