i use project x hl in my irons but for the af901 i opted for the ut machline shafts. cannot go wrong with this combo. others will attest to this as well. i have also hit it with the stock machline shafts it is pretty good as well but i do prefer graphite on my hybrids and this is essentially one:) i have heard people putting nspro750gh wit great success.
my advice is to experiment. give the shimadas or ut machline a try. either way you cant go wrong,good luck