[c-nsp] Replacing a 7206VXR w/ NPE-G1 with Sup720-3BXL w/ WS-X6408A-GBIC

[Matthew.Coleman-Hamilton at servicebirmingham.co.uk]

Hi,

Our Internet BGP tier is currently provided by a pair of 7206VXR routers 
with NPE-G1s which are getting quite long in the tooth. We've recently 
been able to reclaim a pair of Sup720-3BXLs and the associated 6509 
chassis'. Its our intention to retire the 7206s and replace them with the 
6509s /w Sup720s but we require 6 GigE interfaces per box. We have a pair 
of WS-X6408A-GBIC 'classic bus' linecards on the shelf (no spare 65XX or 
67XX modules unfortunately) but my question is whether using the 
WS-X6408A-GBIC to provide port capacity is a good or bad idea in this 
scenario?
I appreciate that using a WS-X6408A-GBIC means that the classic 32Gbps 
shared bus will be used (with a max of 15Mpps per system) but in raw 
performance numbers this is a significant increase on the 7206VXR/NPE-G1s 
~2Gbps backplane and ~1Mpps forwarding rate.
My real concern is that I've found two different Cisco documents that 
describe the Forwarding-Engine Architecture differently for classic 
linecards.
This link :- 
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/product_data_sheet0900aecd801459a7.html
states that "the Supervisor engine CPU makes forwarding decision"
and this link:- 
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/product_data_sheet0900aecd8017376e.html
states that "Centralized Cisco Express Forwarding engine located on 
supervisor policy feature card (PFC) makes forwarding decision"
As the 6500 series is a hardware-based platform I'm keen to make use of 
hardware-supported features where available and not experience unexpected 
issues from high CPU utilisation.
Can anyone confirm exactly how traffic will be forwarded by the 
Sup720-3BXL with a WS-X6408A-GBIC in the chassis?
Thanks in advance, 
Matthew