Just sharing a little tip, mostly for beginners.
According to some topics on Andy's forum (loudness war or something like that) de RMS level of commercial recordings (Mastered) for metal is about -8db (may be more, may be less).
Voxengo SPAN is a free VST that allows you to know the RMS level of your mix, so you can have an idea how "Loud" it is compared to industry standards.
This picture shows what i'm talking about.
Use this plug-in last in your master buss FX chain, so you can check the loudness after the limiting or clipping is applied.
You can download it here:
http://www.voxengo.com/product/span/It's free
By the way, do not torture yourselves on trying to achieve those -8 db RMS level. I've found for my recordings that an RMS level between -12 db and -10 db RMS works really well, it's loud, at least for a home recording/mix/master =).