Hi. Here are a few resources.
To compare the Xeon 5400 to the Xeon 5500 (new microarchitecture and platform design) you can use http://ark.intel.com. Here is a specific compare of the top bin processors for both product lines. http://ark.intel.com/Compare.aspx?ids=37111,33083,
To compare performance of these two cpus on many industry standard benchmarks and some applications explore this website http://www.intel.com/performance/server/xeon/server.htm?iid=perf_server_lhn+dp_server
For HP specific data comparison you will need to look at Hp.com. the Xeon 5500 runs in the new G6 blades and the Xeon 5400 runs in the prior generation G5 blades. there is a significant incresase in capability in these platforms enabled by the underlying intel technology ... compare these at http://h10010.www1.hp.com/wwpc/us/en/en/WF04a/3709945-3709945-3328410-241641-3328419.html
let me know if you need anything else. Chris