Are there certain bacterial toxins that play a more important role in sepsis?

Yep. Bacterial endotoxins ( see http://textbookofbacteriology.Net/endotoxin.Html ) and exotoxins ( http://en.Wikipedia.Org/wiki/exotoxin) are important. Botulinum toxin, shiga toxin, tetnus toxin, and diptheria toxin are the most potent poisons known (ok, except for uranium and dioxin). Here is more reading: http://textbookofbacteriology.Net/proteintoxins.Html.
Yes. Mrsa (methicillin-resistant staphylococcus aureus), klebsiella, pseudomonas, to name a few, are some of the more toxic and difficult to treat bacteria producing toxins.