Bo what are your exact specs for your BKII? Draw length /weight?
Sounds like a 50-60# model with a 28" or under draw length...........and its actually 64 ft lbs of KE for 377 @ 277.
You have plenty of KE to cleanly take an Elk, and a solid choice for a broadhead.........IMO yeah you are probably on the light side arrow wise,but it will do the job if you put it where it needs to go with that style broadhead.
Is there a chance that you can up the draw weight as you progress to the fall hunt? That way you can go to a heavier arrow and maybe still maintain the existing speed? Or is it possible to lighten the string up a bit?(lighter peep w/ a string loop.....maybe lose the string silencers altogether etc. )
As you stand right now if you went up to a heavier shaft, say in the 450gr range you will be looking at a new speed of around 255fps +/-....which isn' t bad speed wise. If you are good at yardage estimation then you should have no problem........lots of Elk have been killed with a lot less.
If it was me and I albsolutely couldn' t wring any more out of the bow' s performance by raising draw weight or lightening up the string load by using lighter accessories to gain more speed, then I would probably look at raising my arrow weight to around 400-425grs. That way the speed stays at least in the 260' s and KE and momentum will go up a bit more to help with any solid rib hits.
Make sure that broadhead will shave hair, maybe slide to something like a 3-49 in a little longer shaft length.