There's no doubt the 3.0 is a better drive, and the extra power is a pleasure. Bascially the 3.0 can tow a camper trailer and still match the 2.7's accleration.
But unless you're towing a lot I'd argue you're better off with a lower-kay car and the option for 245/70/17 LT tyres.
In the real world, I can't think of a single overtake I'd have made in the 3.0 that I didn't attempt in the 2.7.
Around bendy roads the limiting factor of the Discovery 4 is road safety visibility and passenger comfort, not the engine. Unlike say a TD5 Defender where you're often wishing you could go faster, but can't. Basically, a 3.0 Disco will not leave a 2.7L behind in twisty conditions unless the 3.0 is driven unsafely.
My 2.7 can, at GVM including a roofrack load, maintain the speed limit up the Adelaide Hills heading towards Melbourne.
Yes, I have driven 3.0s on multiple occasions, including one all the way from the UK to Morocco, around Morocco, and back again. In that situation, speeds of 130 -150km/h on freeways with long hills, I'd be much more inclined to a 3.0. But not in Australia.
The 3.0 is also a better offroad engine as it offer greater torque lower down. But nothing a good driver can't make up for, and there are only certain offroad situations where that's important.
If there was the choice of the extra power with no downside, of course you'd take it. But the extra 40,000km and cost is, in my view, not worth it. Those that must have as much power as possible will differ.
When I bought my 2.7 I knew the 3.0 was coming and decided to get the 2.7 anyway. I'd not driven the 3.0, but knew what difference the engine would make and for me the tradeoff wasn't worth it.
Each to their own!

