Hi Vagelis

Option No2 is by far your best choice.

Buy 20mm Dia 10mm Pitch ballscrews and Gear the Motor 2:1. This will allow you to easily reach 13-15mtr/min rapid speeds even with a heavy gantry and the 20mm ballscrew will help reduce whip. Because of the 2:1 gear ratio your torque will double and also because servos give linear torque they will easily handle the higher inertia of 20mm ballscrews.

You will need to increase the frame strength with some cross bracing to achieve these speeds though has it's very weak how you have it drawn now.
Also with the Z axis looks all wrong.? You will only be able to reach down past the gantry bottom by the length of the tool or how much the Spindle extends out of it's bracket. This will limit your cutting ability and the gantry could or will catch work in some cases.!!

Better if you switch the bearings onto the back plate and put Rails on the moving front plate. This gives you maximum strength and will allow reach down and clearance when needed.