So far, the dual core 1.2 Ghz Exynos chip in the Samsung Galaxy S II has been declared the fastest mobile chip out there by many reviewers, and it's probably the main reason why you would want a Galaxy S II. But it seems that the T-mobile version will not have this chip, and instead it will use a dual core 1.5 Ghz Snapdragon processor. So why the change and how does that affect things?
This change could've happened for 3 reasons. One is that the Qualcomm chip has support for T-mobile's 42 Mbps "4G" network built-in, and the Exynos chip doesn't. Qualcomm has long taken the route to implement the 3G and 4G connectivity options directly into the processors, and it seems that strategy has give them a design win from Samsung on their most popular phone, at least on T-mobile. Whether that is a fair trade-off, it's up to you to decide, but I don't think you're losing that much, and I'll explain a bit later why.
The second reason why this could've happened is because Samsung can't build the Exynos chips fast enough. It's not the first time Samsung has been using either Qualcomm chips or Nvidia chips in some of their other models. It could be that they don't have the capability to build all of them themselves right now.
Another reason could be that they simply want some diversity in their phones. Snapdragon chips were the most popular last year, and they might think some people would want those chips over theirs. Plus, this one is clocked at 1.5 Ghz rather than 1.2 Ghz, so from a marketing point of view, it does sound like the Snapdragon one is better.
But is it really? I think it is, but only on the CPU side, not the GPU side. Samsung has once again managed to put the best GPU in their flagship, just like they did last year with Galaxy S, and it's almost twice as fast as any other out there. But on the CPU side, even if the Exynos chip is based on Cortex A9, which is faster than Snapdragon at same clock speed, the dual core Snapdragon chip still has a higher clock speed, so in theory it should still be faster. But it all depends on how well has Samsung optimized the software for it, and if it optimized it just as well as for Exynos.
So, T-mobile customers, you'll get the better CPU, weaker GPU, and better 4G connectivity. Does that sound like a fair trade-off to you, or would you have preferred the Exynos, with a bit weaker CPU, more powerful GPU, and slower connectivity?