My 2 cents:
When GW was new, it was the general scheme of things that the stats of weapons, etc., generally improved as you went from white to blue to purple to gold. That was also back in the day before Inscriptions, so the inherent mods on weapons were not mod-able.
In those days, purple weapons would generally speaking have a higher requirement or have a much less than max inherent mod, such as 13^50 or HCT 8%, etc.. Gold weapons would have a lower requirement and would have max or near max inherent mods, such as 14-15^50 or HCT 9%-10%.
Purple weapons would also usually have crappier prefix and suffix mods mods on them, but of course, they could always be changed.
Any way, somewhere along the way, during all the updates, changes to chests, and inscriptions, etc., NCsoft (or whoever) futzd around with the stats on weapons so much, that the distinction in weapon color is now almost meaningless in practical terms. I think they basically gave up trying to "fix" it - we will have to wait and see if GW2 can straighten it all out.
(My warrior, for example, has a blue armor 16 Ebonhand Aegis with health+60 (enchanted) and dmg-2 (enchanted) - just as good as any shield).
People still like gold weapons best because they are (supposedly) rarer, but I've had many times when I've gotten a req 9 purple drop and a req13 gold during the same run.
So, in answer to the OP's question - there is no difference, performance-wise, between a purple (or blue) and gold weapon of equal stats other than text color. As someone pointed out, there are a few weapon
skins that change from blue to purple to gold - the Ancient Scythe comes to mind.
http://guildwars.wikia.com/wiki/Ancient_Scythe