I was just thinking about it and remembered that a client of mine was running Flexibility 2.
So I took a look at it.
In the admin on this theme, one thing that will create slow load if your theme has it is the PayPal donation box. This one has it. It's loading the PayPal images through an SSL https which will slow down those 2 requests.
Also the admin theme page on version 2 is loading a few extra scripts necessary for the theme customizations.
On the theme itself, this one is loading a Flexibility copy right image in the footer from their site. That's an extra external HTTP request.
If you have that in your version, simply follow the src link for that image, download the image, place it in your themes images and change the src to use that one locally. It wont save the request but at least it will be local as you don't know how fast it is being loaded from their site and from what I see it's not coming from a CDN.
Another thing is how heavy the theme is. Is it very graphical? If it is and not using sprites, every image is another request the browser has to load.
How is your site using the default theme with your current plug-ins installed?