Ethernet port aggregation between modem (CM1100) and router (R7690P)

Thanks for your reply.

My ISP is Xfinity Performance Plus Internet (download speeds up to 175 Mbps).

The firmware on my modem (CM1100) is V2.01.02.

The firmware on my router (R7960P) is V1.4.1.44_1.3.5.

Even though my internet service is less than 1 Gbps, given that both my modem and router support WAN aggregation, I thought there might be some benefit to connecting them this way--perhaps better reliability and/or redundancy.

I finally found the manuals for both products online and learned the proper way to setup WAN aggregation between the two (enable online first, then connect the two modem ports to the router's Internet port and Port4. After doing so, I confirmed through both products' online interface portals that WAN aggregation status was "active". Unfortunately, after doing so, my internet speed dropped precipitously--not what I expected. 

Without WAN aggregation, my network provides download speeds of over 200 Mbps (must be overprovisioned by my ISP).

With WAN aggregation, my network provides download speeds of just 40-50 Mbps.

I don't understand why this would be the case, but I've decided to give-up on WAN aggregation at this point and enjoy the higher download speeds without.