I just got them. Here is my quick run down.

I measure the Speedy Mini at 13.5" x 9.75" x 3.5" (this is leaving the B&R packing materials in it, which do not add much, but I feel inflate it to its regular size).

The Small Byte is 14" x 9.75" x 4".

Weight by our postal scale is roughly 1lb 4.5 oz vs 1lb 9oz, so a nominal difference. (I removed the packing materials and strap.)

Looking at the outside pocket, both have a pocket (stitched in orange) on the front where you could store come cards. The Small Byte's pocket is a hair bigger. On the large orange pocket that expands out, the expansion, size, and number of pockets are all roughly the same, although the arrangement on the inside varies some. The Speedy Mini has one less pen holder and one less business card slot (2 instead of 3 for both). They both have the same zippered pocket above that, where you could store boarding passes/maps/etc.

They both have the same shoulder strap. The Small Byte has an extra grip padding attached to one of the handles. This allows you to bring the two handles together and it holds shut with magnets (it just picked up a paperclip from my desk). Both have the same flap on the back to slide it over your rollaboard handle.

Looking at the main compartment, the flat bottom of the Speedy Mini main compartment is 1.5" wide roughly. The same compartment on the Small Byte is 1" wide and on the back side. Both seem to have the same padding. The zipper on this compartment only comes down a couple of inches on the side.

The Small Byte has another zippered compartment, between the laptop compartment and the outside pocket. It has less padding, but still has some. There is a divider down the center of this compartment, that has a lot of give. There is not a flat bottom for this compartment; both sides come down and meet a single large seam. The innermost side of this compartment has a padded pocket where an iPad will fit in perfectly, with the long edge of the iPad running the lengthwise of the bag. The zipper on this compartment comes down further, so it will open wider and allow easier access if are storing random things in it.

They are both really nice bags, and very similar, as I think we all knew. Currently, I am leaning towards keeping the Small Byte, since I like the idea of the extra compartment and the iPad pocket is a nice bonus. Note, if you want to carry a water bottle, these might not work. I have a 25 oz Trader Joe's water bottle that definitely does not fit and a 16 oz Dasani bottle that just fits (in the outer pocket of the Small Byte.)

Separately, I was just going to return one of these to a Nordstrom Rack store, but if someone wants to cover my costs (my price, tax, and shipping to you), I would be willing to do that instead.