1921 router spec confusion "...concurrent services enabled up to 15 Mbps"

[SBIT]

What does this mean in regards to WAN bandwidth "...concurrent services enabled up to 15 Mbps"?  Our 1921 router with two Gigabit RJ45 ports and no expansion models has been connected to an ISP cable modem providing 250Mbps down/50Mbps up bandwidth for a couple of years.  Our service was recently upgraded to 500Mbps down/50Mbps up.  This came with a new cable modem to handle the increased speed.  However our tests are still only showing 250Mbps down/50Mbps up.  In trying to determine the bandwidth  capabilities of this router the above spec.  is all I can find.  Doesn't seem to correlate to WAN bandwidth.  Second question.  If this router is topped out a 250Mbps down, what is our upgrade path to support 500Mbps down?  Can this router be upgraded with expansion modules or is a new router required?  Thank you

[Georg Pauwen]

Hello,

have a look at the link attached. The 1921 should be able to handle >250Mbps. Since your up/down speed stayed exactly the same after the ISP upgrade, I would check with the ISP first if they can get 500Mbps to the cable modem...

http://www.anticisco.ru/pubs/ISR_G2_Perfomance.pdf

[SBIT]

The ISP link was the first thing we checked and a direct connection to the ISP's cable modem yielded download speeds in excess of 500Mbs. 

Thanks for the link, http://www.anticisco.ru/pubs/ISR_G2_Perfomance.pdf.  Looked at this before and based on table 1 alone you would conclude the switch could easily handle a 500Mbps down-link from an ISP.  But I read the whole document which lead me to conclude real world WAN speed depends on a whole lot of variables.  I've attached a screenshot that consist of the "show interface" command for the GigabitEthernet0/0 and GigabitEthernet0/1 on the 1921 router.  0/0 connects to our main 3560X trunk port GigabitEthernet0/48.  0/1 connects to our ISP's cable modem.  I ran "clear counters" on all three ports then kicked off a speed test that produced a results of 265.31Mbps down/61.16Mbps up.  I don't see anything in the three "show interface" captures that would explain the slow WAN speed on the routers  GigabitEthernet0/1.  If anyone sees something I'm missing please let me know.  Or any other things to look at.  Thank you