I am printing a portfolio for a commercial photographer (my wife) there a couple different books, both with about 150 different images. Most of them are commisioned work, advertising, editorial and catalog.
There's the issue, from my perspective. When I'm printing individual images that will be viewed as individual images, in other words where each print stands and shows alone, I've never had to do more than one proof print beyond soft profiling. I've got the multiple Solux viewing options, do end to end profiling, and am very careful even about the color temp and brightness of my working light sources when soft proofing - eyes adapt quickly to new inputs, and when I got really focused on squeezing all variability out of my environment, the value of all the obsessive focus on profiling and profiles paid off. Where I will sometimes need to make an adjustment it's almost always a problem with shadow density, which is the hardest thing to get right on an LCD no matter what you paid for it, but I use relatively few papers, and have been able to eliminate even that one proof in most situations.
However, books make me crazy, because each image does NOT stand alone. From a creative perspective, I usually optimize every photo to make it the best possible image on its own - most of my printing is for shows or sales of individual images, and whether I chose to shift white balance a bit for one photo versus another isn't an issue, and I am as free with creative color adjustments as I was when I did wet printing. But when I have a series, or a book, where all the shots from an event or project will be shown together, I find I end up re-processing the RAW files with a standard stored setting - which basically shifts the pain from adjusting to get the proofs to match up to having to reprocess the images from scratch. If that wasn't possible - and I have thankfully not had to produce anything that was based on work across years of time, camera types, types of image, art director influenced styles, and film with digital - I think I'd find myself in proofing purgatory even with my obsessive workflow. (I can't tell you how hard I try to avoid that situation... some of my work from a few years ago never gets into my portfolio books any more because I don't want to face Ektachrome VS mixing with my current digital.) Sounds like that's where you are. Really, the answer on how many rounds probably depends on what kind of product you're producing.