It's not going to be 20-30% on the CPU side unless it's an incredibly memory centric measurement. It will be a substantial gain on the power side however.
The leaked presentations put Cherry Trail at 2.7GHz with Burst which is a 12.5% increase in frequency. 7-8% IPC gains(compensating for the fact that frequency/perf increase is not linear) should get 20% on the single thread side.
On multi-thread side 30% would be possible if the sustained frequency running at 4 cores is higher. Multi-thread is only 3x the speed on Bay Trail vs previous Atoms when IPC gains + frequency + double the cores should result in near 4x.
Of course it would be a sore disappointment if they don't achieve 20-30%. Ideally they should be 50% faster but whatever. They think ARM vendors would be incompetent as AMD and would eventually run into "limits"(like power and process...). Not that they won't, but the competitors seem to be doing pretty damn well for being nearly 2 process generations behind don't they?(which also puts into question whether Intel is being true about their "process advantage").
Hm. What I saw/heard was that the BOM was the smallest of gains.
That's supposedly the point contra-revenue addresses, and something they want to gradually eliminate it, the point of nil by 14nm(Cherry Trail+) timeframe.
If you for example want an platform that needs to be fit for both PCs(like Netbooks/Notebooks), and Tablets you'd add necessary adjustments for both SATA and eMMC interface. Their argument was that it was a cost adder, and making it Tablet-only(eMMC) would reduce the cost. And there's other things like most laptops having somewhat user serviceable parts, while on Tablets nearly everything has to be done on a manufacturer level.
Flexibility = cost
The GPU side is going to be easily more than 50% in most scenarios,
I think anything less than HD 4400(which is on 15W U Haswell chips) will be a disappointment. Even with that, Nvidia with TK1 won't be terribly far behind. With rumors that Broadwell class GPUs and 14nm should bring 4x perf/watt improvements.