Is it possible to use 4G LTE routerboard in "bridge mode/no firewall?&Which miniPCIe or USB 4G LTE modems are supported?

I recently purchased a RBM33G and had a tough time getting the Dell EM7455 working in the miniPCIe slots, so I ended up putting OpenWRT on it and managed to get it working, but it’s performance is worse than AT&T Velocity hotspot (roughly 43mbps vs 81mbps).

Is there a list of working/compatible 4G LTE modems for any mikrotik product as well as my RBM33G?

Also is it possible to have bridge mode/IP Passthrough on the 4G LTE RBM33G?

I’d like to leave all routing/firewall/NAT to my CCR1009.

Speedtest of RBM33G (OpenWRT) w/ EM7455 on AT&T 4G LTE: http://www.speedtest.net/result/7595762605 (43mbps)

Speedtest of AT&T Velocity (ZTE) Hotspot: http://www.speedtest.net/result/7593376962 (81mbps)

Here is a diagram of my networks at my home business: