high end PC

If i were you i would'nt go with any of those brands unless you've got lots of cash to burn. Look for less known companies, such as your local PC shop, however if you are getting one of them try looking for individual component benchmarks they should help yuou compare the systems and help you see what changes could give you more performance. Generaly though if the components are the some or have the same specs (alienware 1000w PSU compareed to an Enermax Galaxym 1000w PSU) they'll give the same or very similar performance.

Nomec, although building your own system is fun and can save some money, as mentioned by mm_vr and markop20033, buying a ready-made PC is not too bad.
You can save a lot of trouble, get a package of essential software including Windows, and get an easy plan of warranty.
A trustworthy company can satisfy you, and it is good that you know some of them.
The price will not be too different from one company to another, so you can just focus on the price.
Please note that these ready-made PCs are usually of bad display cards. Some of the companies like Dell would allow you to specify a display cards.
This is necessary if you want a good audio-visual entertainment experience.
Hope this can help you.

What is hi end for you? What you will use the computer for? Work or gaming? You need pc or workstation, best thing to do is making up your mind on the configuration, than look for brand pc/workstation vs. self build price and than making the choice. If you will go for self build I am sure that any local store will be more than happy to build hi end system for you. We can help with the configuration, if you will specify your needs and budget 