Why would memory usage be a predictor of any of those? The actual size of iOS 8 is about 1.1GB to 1.4GB depending on the device it is installed on. The rest of the memory consumption is Apple included Apps that are installed along with the operating system that make the device what it is. . . iOS is actually very parsimonious of space and very good at memory management. Far better than Android. iOS handles all of what requires 2 or 3GB of RAM in Android in only 1GB or 2GBs. The critics keep comparing RAM in the iPhone and iPad against the larger allotments in Android devices. . . but ignoring the greater efficiencies in the Apple devices that simply don't require the larger RAM allotments.
You want to compare performance? That's been done in the bench marks. Samsung and several of the other Android phone makers were caught TWEAKING their benchmark routines to cheat the numbers. Apple never has done that to get faster numbers. Right now, Apple's 64bit Dual Core A8 processor is blowing away the four core processors used in Android devices.
Here is one of the supposedly top Android phones for performance. . . and the geek bench marks:
Basemark II is the only benchmark in which this Android phone slightly exceeds the iPhone 6. . . and that's because it includes a battery test and this Android phone has a battery that is almost twice the capacity of the iPhone 6's. That, however, is not what we are talking about here, we are talking about speed and performance in graphics. . . and the iPhone's dual core exceeds the Motorola's FOUR cores in every test, most of the time by wide margins. Even in the multi-core test, the iPhone was marginally better with two cores, than the Android was with four.