Why drop Siphon Life? It's a great tool if you slot it properly - it damages foes whilst lowering their accuracy and at the same time it adds to your health. What's not to like? I use it as one of Maxigirl's primary attacks, and it's served her very well indeed for 43 levels. If you want to drop an attack, get rid of Shadow Punch. You shouldn't need to take that at lvl 20.
And why take slots from Fast Healing? I'd leave them in.
Soul Drain is marvellous - DM 's accuracy can be tragically poor, so slot SD for recharges and To Hit buffs.
Dark Consumption is good, but I went the Swift/Health/Stamina route so don't feel the need to exploit it as a primary attack/source of endurance yet. It will aggro mobs, but costs nothing but time to activate.
Personally I prefer the Leaping to the Flight pool for this build. Combat Jumping is a much needed extra defensive power, and you don't need Air Superiority - as good as it is - with the other attacks you can call on. Also, Superjump is less slot-hungry, faster, and way cooler than Fly

And you can still use it to take out Skiffs in Terra Volta and Striga
For the future, at 32 I heartily recommend Midnight Grasp and at 41 Focused Accuracy from the Body Mastery epic pool. Slot FA 3/3 with end redux/To Hit buffs, and you can save the Accuracy SOs in all your other attacks - the only accuracy SO i keep is in Siphon Life, along with 1 or 2 recharges (I can't remember which

), 1 heal, and the rest damage; I hardly ever miss with that, and with Soul Drain going I can repair damage fast while swatting bosses.
There's a good, if 6-month old, DM/Regen guide on the US boards
here - although even she doesn't much care for Siphon Life either - are they all INSANE!!???
If you want I'll post Maxigirl's build - she's very good at PvE nowadays, but if PvP floats your boat, DM/Regen is not, to the best of my knowledge, the best PvP set you can have. It is, however, one of the most fun of all my 22 alts builds (yeh, I had to delete a couple to prepare for the new powersets in I7

)