Running Arch on an overclocked PC is totally fine provided that the PC is stable at the overclock settings. There are several programs available to you that will help you stress test your system. The steps of overclocking a PC are beyond the scope of this article, but there is pretty inclusive guide written by graysky on the topic you can read at your leisure.
A very good program for stress testing your memory is [Memtest86+]. It is based on the well-known original memtest86 written by Chris Brady. Memtest86+ is, like the original, released under the terms of the Gnu Public License (GPL). No restrictions for use, private or commercial exist other than the ones mentioned in the Gnu Public License (GPL).
You may download it from the webhost of memtest86+ [here] either as a bootable CD ISO or as an pre-compiled bootable binary. The later can be called by GRUB with a minor modification to your menu.lst to allow you to boot directly into Memtest86+ without a CD/DVDROM.
Either download and burn the ISO to a CD and boot from it, or follow the instructions in the next section to add an entry to your GRUB boot menu. Either way when you enter Memtest86+, the application begins testing your memory without your intervention. It will run indefinitely until you stop it reporting any errors as it goes. When it has completed a number of iterations without errors or runs for an arbitrary amount of time without errors, you can pretty much call your memory "good" or "stable" at the settings you have chosen for it in your BIOS.
Stressing CPU and/or Memory
A very good program for CPU and CPU/memory stress testing is [prime95]. There are both x86 and x86_64 version for Linux you can freely use for stress testing purposes under Linux. Prime95 under torture test mode will preform a series of very CPU intensive calculations and compare the values it gets to known good values. The theory is that if your system is sufficiently stable to get the right answers, it should be stable to most anything you will throw at it. Prime95 is pretty much recognized universally as one defacto measure of an overclocked system's stability.
Download either the 'Linux' version (i.e. x86) or the 'Linux64' version (i.e. x86_64) from the aforementioned website. It is a precompiled binary so once you have untarred the archive file, simply run mprime as you would any other executable under Linux.
$ tar zxvf mprime259-linux64.tar.gz
To run prime95, simply enter the directory you unpacked the archive and run mprime:
$ cd mprime259-linux64 $ ./mprime
When the software loads, simply answer 'N' to the first question to begin the torture testing. The software begins with the torture test, but if you hit CTRL+C you can break out and return to the main prime95 menu shown here:
Main Menu 1. Test/Primenet 2. Test/Worker threads 3. Test/Status 4. Test/Continue 5. Test/Exit 6. Advanced/Test 7. Advanced/Time 8. Advanced/P-1 9. Advanced/ECM 10. Advanced/Manual Communication 11. Advanced/Unreserve Exponent 12. Advanced/Quit Gimps 13. Options/CPU 14. Options/Preferences 15. Options/Torture Test 16. Options/Benchmark 17. Help/About 18. Help/About PrimeNet Server
There are several options for the torture test (menu option 15).
Use small FFTs or In-place large FFTs (options 1 and 2 respectively) mainly for CPU stress testing. Option 2 (In-place large FFTs) are preferred.
Blend (option 3) is a hybrid mode between the a CPU and RAM stress.
Errors will be reported should they occur. Many do not consider a system as 'stable' unless it can run the Large FFTs for a 24 h period.