So lets walk through this from a SV (pure PvE raiding) pov:
Legacy: 40*1.15=46agi, 80ap, 8mp5
S3 Axe: 0 agi, 92ap, 46crit, 15hit, 98armor penetration
So, for personal damage lets convert the whole thing to AP and crit:
Legacy: 46+80=126ap, 1.15%crit, 8mp5
S3 Axe: 92ap, 2.1%crit, 1%hit, 98armor penetration.
If I remember correctly ~100armor penetration = ~20AP thus:
Legacy: 126ap, 1.15%crit, 8mp5
S3 Axe: 112ap, 2.1%crit, 1%hit
While the hit rating on the S3 axe is really a nice thing (especially for BM hunters) it will have next to no use for a SV hunter since many items have hit rating and we only need 6% hit from gear because of 3%hit we can easily get from talents.
Thus for personal damage we can ignore the hit rating on the S3 axe.
As a result one has to chose between 14ap and 8mp5 opposed to ~1%crit.
Seeing this the S3 axe is the better item as long as you do not have heavy mana issues. If you consider mp5 to be worth something, both weapons will be equally good for a SV hunters personal damage.
And then comes expose weakness...
46agi = 11.5AP without blessing of kings and 12.65ap with blessing of kings.
As a rough calculation you can assume that every point of AP boosts the dps of any melee dps class by 0.3
Thus Legacy adds 11.5*0.3=3.45dps for every single melee dd in your raid.
In Kara/ZA you'll usually have 2-4 melee dds in your raid. In 25mans you'll likely bring 7-8 melee dds.
Thus in Kara Legacy will increase raid dps by 3.5*3 = 10.5dps
In 25mans you get 3.5*7=24.5dps out of Legacy for raid dps.
If the S3 axe was the better weapon, the SV hunter would have to overcompensate those numbers with his personal dps.
Assuming a good SV hunter is doing 800 sustained dps in Karazhan he would have to increase his dps by 1.25% to compensate for the weaker EW.
In a raid the same hunter might reach 900 dps because of additional buffs and stuff. However he would have to increase is dps by ~25dps or 2.8% to compensate for the weaker EW there.
Even if the S3 axe might be slightly better for personal dps, the loss of raid dps because of a weaker EW buff will make the S3 weapon the worse choice.
Basically any weapon without a good amount of agility would have to have absurd high other stats to make it worthwile for a SV hunter.
Edit:
@Ieatrocks EW uptime is normally not an issue. A SV hunter will have at least 30% crit raid buffed (a starting number for a bad equiped Kara level hunter) which keeps EW up for at least 90% of the time.
With a early SSC/TK kind of equip I normally reach 40-47% crit raid buffed (depending on whether I have a feral druid / enhancement shaman in my group or not) which leads to an EW uptime of at least 97%. More crit will not increase this by much, more crit is just nice to conserve mana and do more personal dps.
Edited, Dec 7th 2007 12:01pm by Mulgrin