Pretty sure your Disco will not go nearly as far. Stock the Disco is pretty capable. But lift, tire options, recoverability (I mean both the ability to recover and be recovered) and aftermarket support? I think the Disco will get left behind pretty soon. Heck one stick punctures an airbag and you are toast with no options. Switch to springs? you'll wear out your u-joints faster than normal. Tall tires to get meaningful gains in ground clearance? I don't think you can even get to 33s without serious tire rub...
And this is coming from someone who LOVES Land Rover - looked hard at LR3s and 4s, nearly pulled the trigger when the new gen Disco's came out, waited longingly for the new Defender, flirted with grey market Defender 110s...
Anyway - I'm sure you will be happy with both. But for dirty and tough, I suspect you'll find the JT the better compromise. Lucky that you have both!