It seems that none of the manufactures provide specific power consumption data for their preamps. All of the information I've dug up is other users opinions... which can't be verified so I'll offer that my 'hunch/opinion' is that the power requirements will be met at 300', but that the lower resistance of RG-6Q would help. I would also suggest you consider the lower resistance and RF loss of RG-11.
If at all possible, avoid splicing sections together, it increases the chance of water intrusion and added resistance / RF losses.
http://www.3starinc.com/rg-11_coaxial_cable.html