Swapped my offspec to meta/ruin from at 3.2.2 launch. I used Supplicium's math on DP's weight over wrath totem to gauge my effectiveness (
link)
Right off the bat I can see that your trinkets, while great for burst dps, are not the best for providing DP coverage to the raid due to their uptime concern.
Regardless of trinkets, with your current gear, after raid buffs u should be well above the 3200 benchmark, which according to Supplicium is the mark at which wrath totems should be swapped to searing. Additionally there is always your lifetap glyph which would grant you a nice chunk of SP. As far as calculating DP effectiveness goes, given lifetap glyph uptime should be 100%, you might as well be taking this buff into account as well.
Personally I feel that the ultimate determinant for whether to provide DP is whether your caster dps can utilize it properly. IE if your raid runs with strong caster dps then by all means. However as you said you will top5, and if the other casters are rolling in 10-15, then DP's value falls significantly
In the current 3.2 raid scene its pretty easy for a Meta/Ruin lock to achieve ~4300sp with raid buffs, which stands as a significant improvement over wrath totem.