The possible gain values are:
0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4
28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6
-10
So i’d try 43.4 and 43.9 to be honest.
But the difference to a gain of 40 in regards to message count will probably be low.
(also the range difference will probably be negligible)
Hard to say how much improvement can be achieved by an LNA.
You should check this:
What is the Maximum Range I can Get?
If you have buildings close by they can also be limiting.