Would it? If Sinestro makes a fist construct would he make 2? One that's twice as strong?
I'm trying to think of instances where someone's had multiple spectrum rings on at the same time.
Guy rocked Red/Green in Blackest Night, but I can't recall if he interchanged use of them or if the power was combined. Kyle had every ring at the beginning of New Guardians, but had no feats...
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"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
Guy was using a red knife on one hand and a green knife in the other - demolishing black lanterns. But I saw his effectiveness being due to the black lanterns weakness.
I'll have to take a look when I get home, but I think you're right.
Having one yellow knife in one hand and a green knife in the other shouldn't be any more effective against Superman than two yellow knives or two green knives (made by the same ring).
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"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
The purpose was to open up his entire history. And I do think Jake's answer applies: there is a slight power bump but it's not a full scale power add-on. Though, in John's run it seems having more than one ring makes you more powerful. Take it how you will.
The last meeting between superman and sinestro went like this
I'm not sure what sinestro having another ring would do for him when superman tanked his, atrocitus' and larfleeze's explicit killing attacks without flinching.
And if he's already "dead", him not dying from Sinestro, Atrocitus, and Larfleeze attacking in concert isn't much of a feat that you can apply towards regular Superman.
Having more than one ring makes you more powerful. There's ample evidence of that. Just none that suggests that two rings makes you twice as powerful.
If this is current versions, as the pictures suggest, Sinestro takes all three. And he'd take all three without needing an extra ring or an unlimited charge. He's more powerful than he's ever been, including his pre-DCnU history. And current Superman, frankly, is not.
His durability wasn't amped like all BLs. He wasn't even scratched by that combined assault let alone the possibility of dying and sinestro was shown "killing" BLs left and right.