I have a Chinese phone - the Oneplus One. Highly specc'ed and fast as anything out there... faster, in fact! On AnTuTu Benchmark, it scores over 51000. I think the Meizu M4 is faster, but has a very narrow set of bands that it works on, and not good for AU.
It has the basic specs of the Iphone 6+ and LG G3, but came out 6 months earlier. 3GB Ram; Snapdragon 805 (?) processor, the same as the Galaxy S5; 13MPix camera and 5 MPix front camera; crazy big screen; 64GB Storage.
The big difference was that when I bought it in June last year, it cost me $410 landed. My nephew lined up for the iPhone 6+, to pay $1250. Also, OnePlus encouraged every buyer to modify it, with no warranty voiding threats.
I have heavily modified it internally, meaning that it now runs a custom ROM and kernel, which is making it faster, and even more battery efficient (2 days on a charge).
Renato1, when you are talking in your Original Post about not having memory to install things, this is actually referring to the section of memory that is set aside for system applications. Each app that installs, takes a little more of that space each time, and when uninstalled doesn't necessarily delete that data. When I first started with Android, this got me too. It took a little digging to understand why it wouldn't install things, when I still had 10GB of space left.
This is where having Root (system) access comes in handy, especially if your phone is something like a Samsung (or phone company supplied phone - I'm looking at you, Optus). It makes uninstalling bloatware apps a cinch, thereby freeing up the system allocation.
There is a forum called XDA Developers, and has a wealth of information - as long as you can find your phone on there. You say you have a Lenovo ... is any of these yours?
http://forum.xda-developers.com/lenovo
Have a look if you are adventurous. Either way, I recommend reading a lot before rooting/ROMming.