5.0's have the displacement
BUT, the weak point of the 4.6's is their internals... so if you have to replace the internals, you're likely to get a stroker. So, i'd say it's better to get the 4.6 and stroke it to a 5.0 or better with good internals. there are more parts for the 5.0, but the 4.6 isn't really that far behind. Plus, the dual overhead cam (4 cams) motor is really wicked. So, with the more indestructable block from the factory (about 700 hp vss 500 for the 5.0) and then having to put new internals in it, the 4.6 is better.
In conclusion:
For sub 300 hp: 4.6
For 300-450: 5.0
For 450+: 4.6
Although, i'm gonna try and push 450+ from a stock block, stock internals 5.0 in about a month here.
Lee