and I think lower end is kind of a misnomer... these are not Celerons or anything, but neither are they "enthusiast" ships (those would be the recently release Sandy Bridge - E chips). They are essentially the next progression from Sandy Bridge... that is to say they will be better than sandy bridge, but priced approximately the same, but they won't be as powerful as the SB-E which is priced WAY above these.
And Intel's current release schedule (attempted anyways) is to have a new chip out each year... the next chip (Ivy Bridge) is scheduled to be a die shrink, which will bring power consumption down and increase efficiency is called a "Tick" and the current chip (Sandy Bridge) is a new micro architecture using the previous manufacturing process (read die shrink) and is called a "Tock."
The tock is where the new features and bigger increase in power will come where the tick is more of a minor change, but the die shrink inherently increases performance and efficiency...
from the internal benchmarks that have leaked people can expect up to a 15% performance gain over sandy bridge... I think that's good for a tick and I have my dollars ready for purchase personally.. (though if I already had sandy bridge I wouldn't)
I think the CPU performance increase over Sandy Bridge will be relatively small, 6% (maybe a little more) since the architecture is pretty mature and Intel is focusing their attention on Haswell. The biggest improvement will be in the Intel HD 4000 graphics core which is expected to be around 60% faster than the Intel HD 3000. That should put somewhere in between a desktop Radeon HD 5550 and HD 5570.
I prefer to simply wait for "real" benchmarks rather than leaked benchmarks. I consider a 10% boost to be good which is inline with Intel's tick-tock and new architecture releases (usually ranges between 10% - 15%).