I see what you are saying im spanish boy so im testing at time one of the lowest server here and its going really good.
how much will cost all this new server setup and the backup servers?
maybe you could mount a good platform with 2 apache / lighttpd / ngix frontend website and another good server with mysql for the same price

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Its difficult to take a good service with one server, cause as you said u need good I/O of disk and memory too ... but only one server is a very high load.
I work in a company of hosting in spain and we mount stuff like that (but ... i dont recommend my hosting company cause they are expensive xD).
So good luck with the new server setup
If u need any help i can help u