"I'm looking to do standard industrial double rivet shelving and was planning for the shelves to be 30 deep. Ideally each shelf would be 30" Deep x 5 Feet Long."

If the shelves are supported at the front and back they are going to sag over the 30 inch depth if you put anything much on them.

If you add supports in the 30 inch direction to prevent sag, you can locate them to make more efficient use of 4x8 panels.

The only support they offer is a beam in the middle of the length of the shelf.

I debated ply over MDF....but MDF is just marginally weaker for a shelf no ?

The heaviest portion of the shelf will be the bottom shelf on all them. I plan to store all the track tires down there. Each tire on average weighs around 50lbs ....

I've decided to find a supplier stocking 5x10 BBirch
I can get 4 shelves out of it and should be plenty rigid.

"I can get 4 shelves out of it and should be plenty rigid."

Not with tires.
You are going to need some additional support or it will sag.

Do a search for 'sagulator' for a tool that tries to determine shelf sag.

You might want to look at a different type of shelving. There are kinds that allow you to install extra crossmembers for additional support. Of the top of my head I believe Tennsco offers it on some of their systems and I'd guess the other big players do as well.

Look at the diagram on the second page of the brochure. The part labeled 'added reinforcement' is available individually and you can use as many as you need.

http://www.tennsco.com/pdf/zline.pdf

I actually ended up calling the manuf today.

I can add similar beam support in the center , as well as at 1' from both left and right corners. It really determines on the length of the width a what comes predrilled. That's not to say I can't drill more holes to add similar channels.

Tennsco looks similar except no holes. Maybe it fits into a slitted channel....this unlimited to add and ease of adding.

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As far as shelf material - still debating.

Cheap thick plywood as a maybe...
5/8 leftover cherry flooring is a option (I would need to glue planks together and the cut to size)

On the lower shelf, I was originally thinking I would have to run 2X stock to support the load, but after confirming I can add more crossmember support, I'm just going to stick with whatever shelf material I end up using.

Tennsco looks similar except no holes. Maybe it fits into a slitted channel....this unlimited to add and ease of adding.

Pretty much. There's a notch in the end of the support (which is shaped like an inverted V). Just slide it where you want it and then rotate it to lock it in place. It's really nice shelving but can be a bit expensive.

As for your wood, is there any chance of moisture or do you have to clean the material? Then wood (especially MDF) isn't going to be a good choice.

You do not really need to have the added supports tie into the framing.

Just adding wooden strips screwed from the top to the bottom of the shelve will stiffen the shelf material.

Even a pine 1x2 on edge will greatly stiffen a plywood shelf. and of the framing is taller than 1.75 inches you can use a wider board for even greater stiffness without loosing useful storage space.