Don't you finger notes behind the
slide too? If you do triplet pull offs with slide and fingers you can go pretty fast. Listen to some of Kirks' faster stuff. He can rip it. You can also play short stuccato notes with a slide that sound good too. Of coarse, I'm talking about dropped D tuning. I assume that the same applies with open tuning. You are trying for as many sounds as possible in your playing so playing a fast note with a slide is just as valid as a finger. It will sure speed up your playing if you combine fingers and slide looking at how effectively you can get to the next note,finger or slide.
Sometimes just for fun, I will practice slide by playing SRV tunes using just the slide and then both. It is surprising how many of his tunes can be played that way. Great fun.