Alright. For the sake of keeping this debate SOMEWHAT scientific (pass through count on deer is NOT scientific proof...WAY too many variables head type, sharpness, shot location, size of deer, ribs hit etc)
Here is a test done showing arrow penetration in 2 consistant forms of media. Though the media is NOT consistant with deer... the test is to simply show the results of KE vs. speed. Anyone wanting to argue momentum, can post the momentum figures for each arrow (I dare ya )

Look at the following chart:



Arrow #1 while having slightly LESS KE (and a LOT less momentum) actually went SLIGHTLY farther than arrow#2 in both cases.

ALL this test measures is the difference between a lighter faster arrow, and a heavier/slower one, with almost identical KE.

You MAY find a test elswhere that says differently, but this test DOES seem to change only one variable at a time (different wieght arrows with the same KE...OK maybe to things speed and momentum' s impact on penetration)

This test also is limited to the 2 arrows going at 53 KE whether or not higher or lower KE numbers are equally effected remains to be posted. but one thing IS clear. You can NOT accuratly say " momentum is the most important thing in penetration" Momentum was up and down in this test...and didn' t make a noticable differance at all.

BTW....for those interested arrow #1 has about .434lb-sec momentum, and arrow #2 has .534lb-sec momentum which is about 23% more momentum...for ZERO gain.