Larger SSDs are faster?

That's a fairy tale if I ever heard one! 🙂 Even if it could be true the amount would be so small a human couldn't perceive a difference in actual use.

You can observe the specs here.

I've read that they are always faster than traditional spinning platter HDDs and continue to keep the advantage even as the available space on each drive is consumed with data storage. No moving parts means 100x the reliability also. Much faster and stay that way all the way up to being full of data.

My MBA 13 is unbelievably fast with the SSD, and I won't go back to a loud, slow platter-based HDD...
Sly

I believe you may have missed the point of the query.

There may be some confusion in what you're seeing. There is a basic configuration 11.6" Air with 2GB of RAM, a 64GB SSD & 1.4GHz CPU. There is an "Ultimate" model that comes with 4GB of RAM, a 128GB SSD and a slightly faster 1.6GHz CPU. In that respect, the "Ultimate" model is a faster machine... but the SSD is not any faster.

NCQ is a technology that allowed you to queue up read/write commands and allow the drive to execute them in the most optimal order. It is a significant performance boost with mechanical hard drives because it allowed the drive to minimize the amount of times the drive had to seek across the disk. It is almost entirely irrelevant with SSD's as they offer uniform read times across the entire disk.

To the original question: a larger SSD is only faster than a smaller SSD if there was an increase in the number of channels that corresponds with the size increase. ie, if a 64GB SSD only had 4 channels but a 128/256GB SSD had 10 channels, the devices would be faster because they can execute more simultaneous read/write operations. If the number of read/write channels doesn't change then performance should remain the same regardless of size.

That said, there are other factors. The particular model of memory used tends to change as density increases because of manufacturing constraints and can adversely affect performance. There is a reason the super-large SSD's (400-480GB) tend to have slightly lower performance than the mid sized ones.

While I don't think enough is known about the MacBook Air SSD to say for certain, I don't believe there is any significant difference in performance between the various sizes.

I guess the other issue is, without TRIM support in OS X, an SSD will start to slow down as it has less free space (it will still be faster than a standard HDD). If you have a larger capacity SSD, you'll have a little more room before you start to experience this.