I have heard the a7 64 bit chip is just a gimmick. Reason: you need at least 4 GB of RAM to actually and truly effectively utilize 64 bits.
Wrong order of logic. Backwards.
You need 64bit to effectively address and utilize 4GB of RAM or more.
That is only one of many 64bit benefits.
"Desktop Class" cpu in feature-set, not performance.
You could maybe compare performance/watt.
----------
Mobile phone processor can be as fast as desktop processor, even today. The big problem is the power source powered them. You can run A7 at full speed throttle, but it will only last like 1-2 hours usage. Battery tech is stagnant atm, it's still lithium ion afterall. We need nuclear battery now.
Nuclear batteries have incredibly low power output.
A quick google revealed a Lockheed prototype from a few years back providing 25 nanoWatts of power. 25nW!
iPhone currently has a 3.8V, 5.73 WHr battery that provides 10 hours of usage. I think measning 573mW of power draw for 10 hours would get you roughly 5.73 WHr.
Compare 573,000 nW of needed usage to a 25 nW battery supply.