I have been with ServInt 3-4 yrs backed then, their server was slow, really slow. I tried normal surfing to my site takes more than 5-10seconds load whereas compare to others (I switch to share hosting MediaTemple and Site5), both was much significant faster!
But no doubt their support is really good! Thumbs up! I even wanted to go back to them recently but when I surf their site, its still quite slow, hence I found other better option.
Network geography and physical geography are two totally different entities. You probably had less hops to access a website hosted in Dallas than to access a website hosted wherever ServInt has their servers.