Not sure if there is such a document, with the LSP option obviously you have redundancy, standalone you don't. Everyone's situation is different, everyones business is different. How important is redundancy to your business, how importanat is uptime to your business..? With the LSP option there's more a of cost then standalone, can your business afford that. Do you have IP phones or are they digital..? I'm sure there will be more input from others, but this should get you thinking.