270 feet subpanel feed
3% and 5% are there in the form of Fine print notes. These are not enforceable. If your max demand (power used at 1 time) is 100 amps 1/0 will be fine. We would really need to do a load calculation to provide a real value but 270’ 1/0 aluminum is only 4.68% since you have gas cooking and water heater I would guess your demand will be below 60 amps and that would even allow for 2awg at 3.96% so there is no need to go larger than 1/0. : added  Aluminum wire is a must for cost here copper would just be nuts for this.