>Do you mind if I use a script to download roughly 2500 images
Go ahead. No problem.
>search back end keeps whining if you're going through the result pages at even a modest pace
The limits were put in place to prevent DoSing of the archive. Searching requires a lot of server power so anyone could cause a huge load spikes if we didn't limit it.
Current setting I have is 5 search requests per minute, but I can change it at any time to keep server load down. At least it gives you accurate time you can wait until you can send another request so you can script accordingly.