Cube for cube a 4 will have identical torque as 6, as would an 8. (Ignoring boost/compression ratio differences) More cylinders will allow opportunity for more power as it will rev higher.
Example:
'88 300 I-6 - 265 ft lb @ 2,000 rpm 8.8:1 CR 145 hp @ 3,400
'88 302 V-8 - 270 ft lb @ 2,400 rpm 8.8:1 CR 185hp @ 3,800
Actually, a very good comparison as both have 4" piston. Difference: 3" stroke on the V-8; 3.98" on the I-6. One could do the exact same comparison with the Duratec 2.5 V-6 and I-4 and see identical power (170hp) and torque (165 ft lbs) numbers.
That torque difference at 2k rpm is what everyone feels; the V-8 only has about ~85% of torque all the way up to that point. So in the normal driving range, the I-6 has more torque. V-8 needs 4.11s to have same output at same speed (in same gear) as I-6 with 3.55s up to 2k rpm. But past 2k rpms, the V-8 kicks. And with its shorter stroke, it will rev higher making more power (it just burns more fuel doing so).
Here is where things get tough: Do you shift from 10th down to 9th (like my brother's Grand Cherokee does) when the road is anything but flat/wind is anything but calm. Or do you let the turbo spin a couple pounds of boost? Which is better for gas mileage? Which is better for comfort?
A NA engine (gas) is going to get better fuel economy under heavy load as a turbo is going to have to over fueled to keep temperatures down.
I don't think the 2.7 EcoBoost "owns" the 5.4 Triton for fuel economy when towing a load. My 5.0 does better than 2.7 EB under load - e.g pulling a 7,500lb TT. On other hand, I will decline a fuel economy match empty, nor will I accept a max load contest with a 3.5EB. (I've learned to pick my battles)
So, blksn8k is probably correct - if he tows a lot, the 5.3 in his ST is still probably better.
I will be better off with EB2.3 in Ranger: 90% of my driving is empty or nearly so, and that extra mpg for majority, would cover the 2 less when loaded.