We use an extendable carbon pole for our selftacker headsail and find it set at about 6.5 meters to be about right but are still trying some different lengths. At this length it is easy to gibe the pole as it passes inside the furler without adjusting the pole height.

 We have a telescopic carbon pole which goes from about 4meters-6.5 meters Currently we have is set at 5.65 meters ( Mast to tip of pole) which we find works well with our self tacking headsail. We have a topping lift, a forward guy and a aft guy, the sheet runs back to a gennecker block and onto a gennecker winch. We set the forward guy and aft guy to a point forward of the beam before unfurling the headsail. A new sheath box was fitted into the mast below the standard self tacker sheath box. The uphaul goes down to a stainless steel eye about 3 meters below the new sheath box. If you want to use the normal sheeting for the self tacker you can either take the pole off the mast or  store the pole on the mast ( needs to be on the side of the mast otherwise it interferes with teh normal self tacker sheet) or you can leave the pole out and set aft of the self tacker sheet so it does not interfere with that sheet. You need to make sure the pole is high enough that it can not drag in the water if it is on the downwind side. Just let out the guys and use the uphaul to set it 3 or 4 meters above the water. I attached the aft guy to the midships cleat. The fore guys goes through a fixed pad eye on the forward rail and then to the forward cleat.  To gybe the pole you need to furl the sail and change sheets and transfer the guys to the other side then gybe and then unfurl the sail.  Coming from Samoa to Fiji we were getting about 6.0-6.4 kn of boat speed running at about 16kn of wind at about 160TWA with just the standard 63sq meters self tacker headsail poled out. We got better speed with a wing on wing configuration with 2 reefs in the main and the headsail poled out on the upwind side. We are looking at a downwind sail of about 100sq meters which we can pole out in winds up to 20kn which will give us better downwind speed.   

in these conditions, i was quite happy with the trade wind sail from northsail (double sails around the same forestay). If i am not wrong it is 250m2, 125m2 x2...admittedly, i never use it in the med - the conditions are not stable for a long-enough time to make it worth putting it up...you can also use the pole BTW.