I just seem to remember it as a feature in Aperture three (I upgraded from AP2), that Projects could now hold more than 10k or something?
So there is no limit?
Not that I ever heard. (10,000 or 100,000 -- either -- but which do you mean?)
At some point (around 3.2 iirc) I did read an Apple release that said that Aperture could handle more than 1,000,000 Images. (I have since searched for this statement, and did not find it.) Before setting up a large database, I set up a test Library of 15,000 Projects containing 400,000 Images. This ran OK on a machine w. 4 GB of RAM. Occasionally I reload this Library for testing -- I have never had any problems with it.
But that tests number of Projects per Library, and number of Images per Library. I have never tested number of Images per Project. I am one of the ones who recommend that all users stick to "One Project = one 'out-in-the-world' shoot", and thus limit Projects to less than 500 Images. This recommendation arose during the early weeks of Aperture 3, when there were still many buglets in the code. Limiting Projects helped avoid problems.
Those problems have, afaict, been taken care of. Nevertheless, I still recommend keeping Projects relatively small because that is how they were originally planned to be. There are many, many ways to group Images in Aperture. I'm sure there are other equally-good ways to create your groups of >100,000 Images.
Well I've been using Aperture since 3 and I don;t recall ever seeing anything officially putting a limit on project size.
Now while I'm not as fanatical as some posters here who try to limit projects to 200 or 500 images or whatever, I'd be leery of putting that many images into one project.
I realize you say it works for you and you realize that you are using Aperture in a non-standard way but I have to ask why do you do this? I can see no advantage of placing so many images in one project that using projects, folders and albums wouldn't also address.