Javascript performance isn't everything, you have to count gpu performance, the various WebKit glitches, etc. Android 4.x on new hardware (say Nexus) is getting there, but the experience of the same app on even older iOS hardware beats the new Nexus. But the app isn't reliant on heavy number crunching -- it /is/ reliant on other things that aren't specific to the JS engine.
RAM, though while important isn't always the limiting factor. You need to take the device specs, OS version, vendor-specific alterations, etc. in to consideration. And then realize that just because you did your homework on a device doesn't mean the poor end-user did. And unfortunately for Android, there are a large number of devices out there that going to have abysmal performance.
The best way to get into the market is to jump in now. The nexus 7 is so cheap that, as a developer, it may as well be considered cost-doing-business.
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Kerri Shotts
photoKandy Studios LLC
Sent from my iPhone
Twitter: @photokandy