31 lb/min is around 310 crank hp, tops...so roughly 449cfm. Now according to that graph your power is about right, maybe a little high, about 7-10whp.
A vf-39 is roughly 460cfm (don't have an exact number). So it will produce about 7whp more if we are bench racing.
The 19t will outspool the 39 all day, but the 39 has been known to touch 300whp, and 280+ is very attainable.
I'm just using some conversions to make facts. I myself will be going the 39 route, although this is tempting, I just hate not being able to pull to at least 6500
To each his own, and feel free to correct me if I'm wrong.
Hopefully within 2 weeks I'll have a graph for you