Building a Powerful X8

Hello,
It is my first attempt at building a compact (680 mm) multipurpose X8 aerial platform. The idea is to have a system that will go from using a GoPro 3 Black with a 3 axis gimbal to a mirrorless camera (Sony A7R) with a 3 axis gimbal. My current setup is having an issue with throttle control when it is at its lightest. At the lowest throttle settings it shoots straight up in the air and it is very difficult to control. The reason is that at the lightest config both configuration hover around 20 to 25% throttle. I would like to get any tips on how to best tune. Seeing that my heavier lifter will have even more powerful engines. Also using the latest Copter V3.3.3

Current Setup
Motor: 8x 4108-380KV Turnigy Multistar 22 Pole Brushless Multi-Rotor Motor
Esc: 8x ZTW Spider Series 30A Small OPTO Multi-Rotor ESC 2~6S (SimonK Firmware)
Prop: 8x Graupner E-Prop 15x8
Body: Black Snapper Pro L foldable frame
FC: Pixhawk 2.4.8
**Batt:**download Multistar High Capacity 6S 5200mAh Multi-Rotor Lipo Pack (EU Warehouse) (6S3P config)
Weight: 3299g

Future Setup
Motor: 8x KDE4014XF-380
Esc: 8x KDEXF-UAS55 Esc
Prop: 8x KDE-CF155-TP PROPELLER BLADES, 15.5" X 5.3
Body: Black Snapper Pro L foldable frame
FC: Pixhawk 2.4.8
Batt: Multistar High Capacity 6S 5200mAh Multi-Rotor Lipo Pack (EU Warehouse) (6S3P config)
3995 grams

Setting the throttle mid lower should help. details are here on the wiki: http://ardupilot.org/copter/docs/ac_throttlemid.html

Note: I’ve moved the topic to Copter-3.3.