If print quality matters at all, you have to pull a test book. Wait for the discounts and press print.
Spend some time with the book, a couple days at least, and adjust your pictures appropriately. Each of the papers will produce quite different results.
I find in general that the uncoated higher end papers tend to produce weaker blacks, so I pull the blacks down a hair and push some contrast into the shadows, and that works for me. The glossy magazine paper, the cheaper paper, produces relatively sturdier blacks, to my eye. The cheap paper in the trade books is slightly translucent, so if you have a large dark print on one side of the page, and text or a small or a light print on the other side, you're gonna see a faint dark rectangle. And so on and so forth. Your mileage, however, will differ.
Pull a test book and look at it.
I like blurb and do a lot of stuff on it, but it's not High End Printing.