bh and speed are both very valuable for 3 point shooting.
the "against the other slower defender" type of thinking doesnt really work in HD, in my experience. HD doesnt go, wow, this guy is faster, hes going to blow by that other dude. i think instead, they come up with "abilities" - as in, the guard defending you has a defensive "ability" based on his def, ath, spd, etc - and really the individual rating comparisons between players don't have any impact.
3 point shooting is the same way. per, then spd, bh, ath, sta, iq, all factor into your shooting ability. you can have less than exceptional ratings in any 1 category, great ratings in all the others, and shoot a good %. the only thing is you REALLY have to have good per to take and make a lot of 3s (can have a good 3pt % with lower per and less 3pt shots, though).