I've never owned a Hacker, but if that's the way you want to go, you could save yourself some money and go with a Feigao. If you are determined to spend the money, go with a Neu motor. The Quarks do very well with the Neus.

The 7XL is about a 2200kv motor. On 6S it will self destruct. Besides, the Quark won't do 6S very well. Stay with 5S. If you are going to run 5S, I'd go for an 8XL in a Feigao, or either the 1515 2.5D for a fast setup and will run cool, or a 1515 1Y for some insanity.

The 8XL on 5S in my Muggy is just sick.