User blog comment:Zwann/Vasto Lordes in the Espada, let's analyze./@comment-1769234-20100701020624

This topic has been going on since the Vasto Lordes and Espada were talked about and until it is stated this is all speculation though here is I believe.

My opinion on this is that if any were Vasto Lorde it might be Espada 1-4.

My reason for this.

It states that the are humanoid, but it never stated that they are 100% humanoid only it states that Vasto Lordes will make with 100% make humanoid sized arrancars.

1. Starrk he was killed by Shunsui Shikai, but some forgot that Starrk was also in battle even if only for a short while with two Captain level Vizards Love and Rose and Captain Ukitake of the 13 divison.

2. Barragan was killed by his own power turned against him by Hachigen's Kido barriers. Soifon did battle him but didn't prove that he could be beaten by her alone. Soifon could be more of an average captain in terms of spiritual power as with spiritual pressure level her's is great spiritual power not immense. As stated that great spiritual power is most common in average Shinigami captains.

3.Harribel did fight against Toshiro and he kind of held his own against her, but ulimately she was killed by Aizen someone with at least twice the spiritual of an average Shinigami captain.

4. Uliquiorra was killed by a Full Hollowed Ichigo, as before he was in that form he could do almost nothing against him in his first Resurreccion and was nearly powerless in his Resurrecion Segunda Etapa. Side note the shilioutte that Toshiro gave could have been Uliquiorra before he was an arrancar.

Also the rule that Espada ranking 1 through 4 cannot release their Zanpakutos in Los Noches as their releases could do great damage to Los Noches, that could mean that only Vasto Lordes release's fall in that category so the ranking of forbidden release could rank from none to all of the Espada or to a few of them.

These are all my theories with facts from their past battles before they were killed.

Another thing is it is said that Vasto Lordes are stronger in battle skills than average Shinigami captains. Now that could mean anything the might have slightly stronger spiritual pressure or have abilities that are strong or they could have all that and much more this remains to be seen and more importantly heard.