Ah yes, I remember this one.
I believe the recommended limit was 20k-50k/hr for each one. It's possible I wrote it down in my guide: slideshare.net/jdavidhill but it could just be the link to the old article.
While is good practice to adhere to some form of delivery rules - I am not sure the ISP loads / sends are as valid as they once were. Marketo used to have a terrible reputation for "Spam" but this has cleared in recent terms with the shared servers listed only a few times each day (and mostly on smaller RBL's)