What speed should a PC be used at ?

I want to make sure I use the right speed on my PC so as not to creat any swirl marks .

Depends what your doing and what pad your using - for polish/swirl mark removal you should use 5~5.5 for wax/sealant 3~4 - you won`t create swirl marks with the PC as long as you follow the guidlines for thr product used. :)

well, im not as experienced as many of these guys here, but ill just give you my view anyway. for polishing, i like to go at either 5 or 6 (im a real speed demon!!!). As for waxing, i just like to go by hand

A good rule of thumb I have learned is the rougher the product being applied, the slower I should use. On my Buffer for instance, compounds 1500rpm--polish at 2100 -- and glazes at 3k

I have found that with diminishing abrasive polishes like DACP, Poorboys, etc. that a speed of 5-6 works best because it generates enough friction to allow the abrasives to break down properly. I have found that running it too slow with the more abrasive products will sometimes cause slight scratches because the product does not break down.
For Sealant application (UPP, NXT, etc.) I use a speed of 3-4.
This may change for you based on how much pressure you apply and how much product you apply to the pad.

You guys crank those PCs up!!! I always do a medium polish at 5, polish at 3, and apply sealant at 1. Do you think I`m doing something wrong?

If what you are doing works ... then you must be doing it right.
Since we don`t have pressure gages and speed monitors attached to our arms and don`t measure the product applied to the pad in micro ounces ( I know not a term), everyones processes are going to vary some ... what is important is finding what works for you and repeating it over and over and over!