See second question's answer...
Same as your que: http://www.cisco.com/en/US/products/hw/routers/ps380/products_qanda_item0900aecd8028a982.shtml
I am giving you here both for QOS for your better comparision.
851 only support :
Quality of Service (QoS) Features
? Weighted Fair Queuing (WFQ)
? Policy-based routing (PBR)
? Per-VC queuing
? Per-VC traffic shaping
Q. What QoS features are supported on the Cisco 870 platforms?
A. The Cisco 870 Series supports advanced QoS features on the WAN interface to strictly prioritize different types of traffic, especially voice traffic. These advanced QoS features include Class-Based Weighted Fair Queuing (CBWFQ), Low Latency Queuing (LLQ), class-based marking, policing, Class-Based Weighted Random Early Detection (CBWRED), Network-Based Address Recognition (NBAR), QoS preclassify, prefragmentation, Resource Reservation Protocol (RSVP), Priority and Custom queuing, and LFI. Starting with Cisco IOS Software Releases 12.4(9)T2 and 12.4(11)T, DSCP and IP precedence marking are also supported on the LAN using the switched virtual interface (SVI).
Q. What QoS features are supported on the Cisco 850 platforms?
A. The Cisco 850 Series supports basic QoS features, such as weighted fair queuing (WFQ), policy-based routing (PBR), per-VC queuing, per-VC traffic shaping. NOTE: Cisco 850 does not support the advanced QoS features listed for voice.
