I have run the Sonnox Oxford SuprEsser plug-in in a Pro Tools HD context, so I didn't have any problems at all running it. I don't think that I've ever had a need to run more than two of these plug-ins simultaneously anyway, and if you're going to need that I would recommend printing your tracks anyway. I can't really say how well this would run on your LE based system, as it just depends on your configuration.
To date, the Sonnox Oxford SuprEsser is the most in depth de-esser I've seen. I don't have it in my home system, although I wish I did as it can do more and sounds better than the de-essers I have right now. While perhaps not the most pressing plug-in need, having a great de-esser can really pay off, especially one like this where you can get really specific with what you're doing. While certainly more expensive than just about any other plug-in out there like this, it also can do a whole lot more. If you're someone who is looking for an advanced de-esser, look no further than Sonnox's Oxford SuprEsser.