How much block value (not rating) should a tank aim for when facing a boss like Prince in Karazhan?

My current amount of damage blocked is between 270-295 depending on item choices I make - usually I will stack dodge in preference to a block value item (ie. Boots of Illusion) without gimping my block value too much. I think my block value is too low for Prince... is this right?

(items i substitute are: T4 gloves, Boots of Illusion & Lion's Heart Girdle)

Clapton (Dath'Remar)
Health: 14,044
Armor: 15,312
Defence: 498
Dodge: 17.86%
Parry: 17.02%
Block: 24.54%
Resilience: 48
Expertise rating: 11
Hit rating: 25