A better option for you: Call Dell or HP business consultant and ask what they recommend for your specific type of workload.
Then you can either go with their suggestion or find similar hardware on your own.
Ultimately you should contact a sales consultant. what type of application is this? What type of requests would this application handle? what operating system will be running on this server? how much data would be transferred when a single request is processed? over what network would the application run? Do you have a Gb back bone?