ok here goes, i will try and give you the essentials of each and the benefits.. i have driven gts with all or none of the options you question in both 335 and 550 engines... if you read any o f my posts you will fnd that i do seek the ultimate drive from my bmw and my opinion is likely to show through in this post...
DDC, gives you essentially ride only characteristic changes...from a soft and squishy ride in comfort to firmer suspension in sport...note ddc effects the suspension for the most part look at it as adjustable shocks...it is not interactive with your driving...on comfort its soft all the time until you take it off of comfort...in sport its stiffer all the time until you take it off..
DHP dynamic handling package, is far more...it incorporates the concept of DDC but it is active (Adaptive Drive), the car adjusts to the road the stiffness or softness fluctuates with the road. DHP also includes ARS (active roll stabilization) utilizing stabilizers in the front and rear corners to work with the now adaptive shocks to stiffen or soften each corner of the car INDIVIDUALLY!!!! this greatly reduces body roll in the corners, nose diving when braking, rear squating on hard accelerations...and overall makes the car handle like a bmw should. it also incorporates a different shifting pattern to the engine in tune with everything else, definitely quicker as well..... there is no comparison in the handling of the car with DHP!
Lastly integral steering....a completely different issue...NOTE NOT AVAILABLE ON ALL WHEEL DRIVE!! it is pretty cool once you get used to it...however not nearly as important in my opinion as DHP... IAS at speeds below 30 mph, small turns of the wheel give you more turning the you would think...great when yo need to do a lot of manuvering at low speeds and above 30 the steering tightens up... BUT the big thing is the turning of the rear wheels.. at speeds below 30 the rear wheels turn in the opposite direction from the front wheels making u turns in far less space possible for example.....very very cool with such a big car as the gt. but even cooler is at speeds above 50 (i think its 50) the rear wheels turn in the same direction as the front wheels (only 2.5%) but it is very very noticeable...at 80 mph and above changing lanes feels like it is a horizontal move....IAS does also reduce body roll in turns or quick lane changes even more then DHP alone...
As i have said in a number of my early reviews as well as my 10K review... the GT deserves DHP and any one driving it with and then without will wish they had opted for it...
hope this helps... come join the club...still one o f my favorite cars i have owned....
2012 GT 550ix Msport (feb12)(ok early march 12)
09 X5 4.8
12 X3 35i (the wife)
61 356 roadster