What is the output buffer size of a GigE port on a Cisco GSR 12012?

For the past few months I've been baffled by the buffer size of a GigE port on a Cisco GSR 12012. When I type "show interface xxx", I see many lines, but no line states the size explicitly. The only line that alludes to the buffer size is output and input queues. Considering the fact that GSR 12012 uses virtual output queueing, meaning that most packets are actually queued at the input port, I could add those two (40 + 75 in our case) and multiply the sum by MTU 1500 bytes and get 1,380,000 bits or 1.38ms worth buffer. However, delay we have measured varies anywhere from sub-milliseconds to tens of milliseconds. And I don't know what the maximum is.  

Some friends showed me a diagram of the packet forwarding engine that has CAR (committed access rate) - CEF (Cisco Expedited Forwarding) - WRED - CoS - MDDR (multiple dispatcher with direct routing) before a packet hits the switching backplane. All of them seem to pose loss opportunities to me. One of the friends suggested that the buffer size on a port must at least be 512MB, because in that complex chain of control, 29 bits is used for memory access (29 bits = 512MB) which far more than 1.38 Mbits.

Due to virtual output queueing, as packets are held back at the input, does the (virtual) output queue size grow as more input ports are added? Let's say the buffer at the input side is 1MB and there are 10 inputs ports, then the overall virtual output queue size is 10MB? If 20 input ports, then 20MB?

My question is: Which of the above three is correct? What is the output buffer size of my GSR 12012?

---------------------- "show interface" output -------------------------------

GigabitEthernet3/1 is up, line protocol is up

  Hardware is GigMac 3 Port GigabitEthernet, address is xxxx

  Description: ===== xxxx =====

  Internet address is xxxx

  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, rely 255/255, load 239/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex mode, link type is force-up, media type is LX

  output flow-control is unsupported, input flow-control is off

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:07, output 00:00:07, output hang never

  Last clearing of "show interface" counters 1w0d

  Queueing strategy: fifo

  Output queue 0/40, 0 drops; input queue 0/75, 0 drops

  30 second input rate 710378000 bits/sec, 113901 packets/sec

  30 second output rate 975842000 bits/sec, 124259 packets/sec

     61597200223 packets input, 46298292870948 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

     487 input errors, 0 CRC, 0 frame, 487 overrun, 0 ignored

     0 watchdog, 0 multicast, 0 pause input

     68237350042 packets output, 70308246946400 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 babbles, 0 late collision, 0 deferred GigabitEthernet3/1 is up, line protocol is up