WotLK Classic Frost Death Knight Stat Priority

1. Hit/Expertise to cap;
2. Strength;
3. Armor Penetration;
4. Critical Strike;
5. Haste.

Hit and Expertise cap are crucial for Frost as Runes can be a very limited resource and your main priority should be getting the most out of them. Frost Death Knights typically dual wield, and being able to reach these caps allows you to take full advantage of the additional auto attacks generated by having a second weapon.

Strength is the best pure DPS stat for Death Knight as it increases Attack Power and Critical Strike. You also rarely have to sacrifice Strength for another stat are you often have to do with secondary stats.

Armor Penetration increases the Physical damage you deal to targets up until a cap that will not be realistically obtainable until Icecrown Citadel. The vast majority of Frost's abilities deal Physical damage and benefit greatly from the reduced Armor you will be attacking thanks to the Armor Penetration stat.

Frost synergizes extremely well with crit thanks to talents like Guile of Gorefiend, but also due to the increased amount of auto attacks you will be doing by dual wielding crit gains a bit more value from that as well.

Haste increases the frequency of attacks, which is great for Frost as it can greatly increase the amount of Killing Machine procs in a fight and leads to more applications of Rune of Razorice.