Hey Gary, I moved to Austin in the 70's and have mountain biked Barton Creek more than a few times; great technical trailwork and water when there's not a drought
. The Neo Cross is a great riding bike; however, that motor is not strong enough for your size person and that trail. The smaller 36V battery might be a concern, since you're gonna burn through more power off-road.
The Stromer ST-1 might be a possibility; however, that bike generally comes with a 36V, 396watt/hr battery and this bike is heavier than the Neo Cross and other mid-drive style bikes. If you can get it configured with their 36V ST522 battery (522watt/hr) then you'd be a bit more secure having adequate range. Still this bike design is primarily street, so it all depends on how much time you plan to be on the trails.
Take a look at some mid-drive, 48V systems, like the 2014 IZip Peak, with the TransX drive, which has phenomenal torque--interpret that as-Hill Climbing, Yeah! (2015 isn't available yet, but when it arrives, it's a full suspension bike) or the Haibike XDuro RX 29er with the Bosch mid-drive system. Both of these bikes have 48V down tube mounted batteries, so your weight distribution feels natural. And they weigh less than your average ebike, only 48lbs.
Another, less pricey option that would have the power, range & frame strength that you need might be Prodeco Tech's Phantom X-3, with the 500watt hub motor & 36V 16ah Lithium battery (that's a hunky 576 watt/hours of juice). This bike, like all of those mentioned comes with hydraulic disc brakes; a plus for trail riding. Down side, rear mounted battery, throttle drive rather than pedal assist, but a lot of bike for the $$$$!
Whatever you choose, just get out there and ride--Austin is blessed with a number of great mountain bike trails and several local mountain bike clubs,