as you said, FM12 could keep the images outside the DB, storing just the reference path, So, performance will depend on the number of records, in your case images, not on the size.
In FileMaker 12, you have two options to experiment with: External storage and selecting the "store a reference" option when inserting the image into a container field.
I looked around and it seems like the Supercontainer is what I might want to use. I need the images on FMGo and I do not think referenced images will show on the iPads.
This is currently only needed for a LAN. I did a test and started duplicating a bunch of records and trying to get it to slow down. It worked ok even with a large number of large images. There is some delay in loading all the records in table view. Considering I loaded the database with an additional few years of data for testing it should be ok for a while.
If this becomes an issue in the future I will deal with it then.
If you are using the iOS devices as clients of a Hosted database via WiFi, externally stored images should work for you.
If you have to physically copy the database onto the iOS device, you have other problems as your file size will quickly exceed the capacity of your iOS device unless you set up a system that only downloads a portion of the data to it for syncing back to the main database at a later point in time.
There are sources online about Filemaker Optimization
A free Filemaker Developer account allows access to a forum for developers
A LinkedIn group http://www.linkedin.com/groups/FileMaker-Optimizers-4001870
The developer resources are looking good. Thank you for the insight. I definitely have some design decisions to make. Those are the most difficult.
Just to add a rant I ordered new iPad 4's that arrived on 11/21. On 11/22 I get the news about the iPad air with faster processor and faster connectivity which is exactly what I need in a situation like this. I suddenly remember all the times I pointed the finger at others for not waiting just a few weeks more for the latest hardware. Now its my turn, haha. I am upset but laughing about it at the same time.