To go faster, assuming flatish water and best deep downwind angle (around 130 Deg off the wind):
- More wind

optimum is mid to high 30's, but at Lake George it's probably 5 knots lower for the same speeds as it is super flat and you can chose your angle very easily.
- A narrower board for your weight (CA40, Mistral 41cm, Starboard 44cm etc). I switch to CA40 and 5.2m at high 20's.
- Assy fin does help as you can confortably sail a smaller fin which = less drag. The Tribal assy 18cm is at least equal lift to a symmetrical 20-21cm. and still gets upwind pretty well. I use the 16.5cm Tribal assy quite a lot.
- Go a smaller sail when powered up. I am close to your weight (72-74KG) and have my fastest speeds on 4.4/4.7m, 5.0/5.2m. A smaller sail set deeper is lighter on the board allowing to to 'fly' higher and still has the same power as a larger, heavier sail set flat for control. Larger sail also has more drag. There is only a certain amount of power you can balance with your weight. Sure, you can downhaul and flatten your sail out to maintain control, but then you have too much drag and weight on your board. The one type of conditions where smaller board, sail and fin is not so cut and dried is when the wind is up and down a lot and you need to be able to sail through the lulls, but in my experience, not many good speed spots really require that.
- The newer KA Speed sails are deeper and more powerful for their size than the Koncepts of a few years ago. For your size, use them on an RDM mast.