Would that be covered under UX? Loading speed seems like something that would be under the UX heading, at least it is as I understand it.
Also, when we started to model pedestrian traffic, we also began to start on the long road to releasing software so that we could sell the software and the companies could model their own traffic. (Many companies consider such data to be proprietary and it can be difficult working for them because of their protective nature.)
We were able to get consultation through Jacob Nielson. He was still fairly new to the game (early 2000s) and things like eye tracking were just coming into the fray. I wasn't able to attend any of his meetings and didn't have much to do with the specifics.
But, my employees were happy with him and our customers were happy with the results. He's mentioned in the article by NN Group, which is Nielsen Norman Group.
The employees were happy and, as mentioned, so weren't our clients. They were also able to take what they learned and apply it to our internal applications and processes. (UX is much more than UI.) This, in turn, helped us more than what we'd expected. I distinctly recall QA being happy with a number of changes.
But, it points to the value of good UX and the benefit of getting a professional to consult or, perhaps, directly on staff.
Because of my lack of direct involvement, I'm not going to specifically recommend them - I don't feel as though I'm qualified to do so. I will say that the results were very good.
We'd chosen them because one of our employees had been following their site and was very impressed with the work they were doing with regards to web sites. It was that same employee who had recommended we get a UX consultant in, in the first place. Given the results, I am happy to have listened.