I'm not at all sure that for this purpose you have to go to an 11x14 book.  What you will deliver to models is 9x12, and that's what model agencies are used to seeing.  I think it's entirely acceptable - even expected - for test photographers to use 9x12.

Another thought:  you will be judged by the team you put together, not just the photography.  Your makeup artist has to be agency-quality, as does the hair stylist and wardrobe stylist, if used.  In addition, the models have to look like agency models.  While it may not be fair, every contributor to your portfolio will be judged.

That's interesting about the size - that wouldn't have occurred to me but it makes sense in context - so the bottom line is that the best way to show you can really shoot this stuff is to produce a book that's just like a really solid model's book, it just happens to have more than one model in it.  And any variation is going to detract from that (which includes not having any expectation that they'll cut you any slack if the non-photographer parts aren't up to snuff.)

Personally I use a 9x12 book to show modeling agencies here in Vegas, it seems to work well and I have received positive feedback on it.

I also leave about 20 or so of my zed cards at the agency, many have commented on it being nice for them to be able to give my zed out to models to see my work and for them to contact me. I restock the zeds if needed when I re-visit that agency.

A few other local photographers leave a 4x6 mini port at the agencies however from what I have seen, people tend to remove some of the images from them so most have blank pages in them.