Not sure if you still needed help with this, but I looked into this a bit and from the looks of it you would want the DW5808. I understand what you're saying about it not fitting but that is because the DW5808 comes in 2 versions, the DW5808e which is a ngff card (which I am assuming wouldn't fit unless there was a revision of your motherboard that I am not aware of), and the DW5808 which comes in the Mini PCI Express (which is the same form factor as the DW5802). Let me know if you're seeing the same thing (I have attached links below detailing this).
Here is an image of the DW5808e that I do not think will fit (since it is NGFF), and here is one of the DW5808 that should fit and even has drivers for your system (under the m6800 model). If you do order the 5808 make sure it is specific to Verizon (I think this is the only version but just just wanted you to be careful).
Let me know if you're seeing the same thing (regarding the different cards), and bear with me, this is not my area of expertise but thought I would try to see if I could help out.