I agree w/ mattjw about power output and servicing, but don't take duc's word for it about Monsters under 800cc. I give my buddy's 900 a hard time, and I've smoked an R6 in the 1/4 on my 750.
IMO it's something only you can answer, because at this point you're splitting hairs. Using something like "real world riding" is an attempt at objectivity in trying to make the decision between the two, and you can bash around pros and cons forever about it - and still never come to a decision. If you want to be objective, how worried are you about maintenance? The S4R by its nature will require more involved maintenance than the S2R. If that's a big issue for you, then there's your answer, I guess.
But my real
answer is this: deciding between these two bikes is entirely subjective. Ignore the rationales, the reasoning, etc. Which bike grabs you by your ass and doesn't let go? Which bike always seems a little shinier in your mind's eye when you think about it? Are you trying to talk yourself into buying one bike, but you can't get the other one out of your head? Well, there's your answer.
If you're still unsure, then you need to use the coin toss trick: Take a quarter, say heads for the S2R, tails for the S4R. Flip the coin. When it lands, if the first thing into your head is "how about best two out of three?" then you know what the answer is - it's the other one.
And post some pictures when you ride it home.