Summoners and Spell Speed

[Myon88]

Spellspeed is not the way to go, it does not buff any of your cooldown or ogcd based damage, and summoners have the weakest valued gcd on average in the game at 120p for ruin 3. Even if you get lucky and that faster gcd nets you an extra cast, 'only' getting an extra ruin 3 is pretty bad payoff compared to what other jobs can do with their gcds. It's not just a matter of it making double weaving harder or not, that's just a 'bonus' downside, even before all that is taken into account, it's just a plain bad stat.

It is true that a faster gcd makes it easier to get 11 wyrmwaves per bahamut vs 10, but that's more a curiosity than a real consideration.
1. It's not a guarantee that a slower gcd can't get 11 wyrmwaves in the same setting
2. You can force 11 wyrmwaves anyway in any situation with an extra ogcd in bahamut (addle/tri-disaster)
3. Even if you did get an extra wyrmwave, you'd need to consider it against the dps loss of the crit/det/dh you lost to get that spellspeed.

In short it's a terrible stat, the speed stats tend to be bad for most jobs in the game. Generally speaking, you should run far away from any items with spellspeed on them.