The ballistics of bows are incredibly complicated - even compared to firearms, where they already sometimes seem more art than science...
However, a few things to consider:
The velocity of the arrow is limited by how fast the limbs of the bow can return to their initial state. This in turn is dependent on may factors, including the material the bow is made from and its mass. Typical maximum velocities range from around 55 m/s to 125 m/s. The higher figures are from compound bows and gain advantage from the cams. This means every bow has an ideal arrow mass - lighter arrows won't go any faster, have less kinetic energy, and just mean more energy being absorbed by the bow limbs; possibly damaging them. Heavier ones will be slower with little extra kinetic energy. The important lesson is that maximum velocity is a property of the material of the bow, not its draw weight.
This leads us to a limitation of accuracy of bows vs firearms - bullets travel much faster so their potential for long range accuracy is much greater. The limit of accurate shooting for bows is going to be 100m to maybe 150m. Beyond that the curved trajectory of the relatively slow arrow is going to mean that you are using indirect fire - literally raining arrows down from above which is never going to be as precise as aiming directly at the target.
Second, bows with very high draw weights suitable for super-humans are going to shoot very heavy arrows. This is a good thing for penetration - heavier projectiles penetrate better all other factors being equal.
Armour penetration is about the only thing that will change at the target however.
Bows with 70lb draw weights will already shoot clean through an unarmoured target with the same body mass as a human at 20m. That is with broadheads. Nobody really shoots arrows optimised for penetration at living targets anymore, but just for the sake of argument lets say 30m. I don't know at what distance a long bow with twice the draw would reliably accomplish the same feat, but safe to say, significantly further. We are now approaching the range limit of practical accuracy. Our super heavy arrows can probably do the same thing past the limit of accuracy, but the maximum damage you can do the target is shoot an arrow straight through it which the lesser bows can already do at practical distances.
The heavier bows will penetrate armour better, but again, in the absence of anyone having tested 400lb draw weight super bows it is very difficult to say how much better... How much do we need?
Breast plates and helms of high quality mediaeval armour could reliably defeat long bows. Other parts of the armour, and cheaper armours provided some protection (lethal wounds became survivable ones - an arrow in the lung became an arrow in the meat of the chest).
If we doubled the momentum of the arrow, which is quite possible, then I would find it plausible that the best armours would offer partial protection, with lesser armours providing little protection, except at long range. This would put the super bows on a par with early firearms, but still far behind even early breach loading rifles. That said, opponents would rightly fear anyone wielding one of these bows...
A note on arrows: it turns out that arrows actually need to be flexible, so unbending is not a desirable property. If the arrows need additional support during firing, then an arrow guide can be used to provide additional support.