My access is generally
My access is generally limited to press events, but Nissan has always been great about making sure we have our hands on the coolest stuff they have available. In less than a quarter mile, the smaller engine will almost always prevail. This is because the fewer cylinders you have, the faster your firing rate probably is and the less time it will usually take for your engine to make maximum output. The sweet spot for torque output in a smaller engine with high turbocharging (ala the GT-R's V6) is at lower RPM than it is in larger engines with more displacement to create their peak torque. Off the line, torque is all that matters and the faster you can get to your highest output, the better. This is why drag racers rev their engines and hold the brakes on the starting line before the green light.
The GT-R's other advantage is that it puts power to all four wheels (all-wheel drive), which means it gets better traction and so holds the road better. It's not uncommon for racers to "break traction" from the start, which you'll see as an observer as spinning wheels, tire smoke, and fishtailing as the car moved forward. With AWD, that's less likely to happen.
Really, though, the GT-R's greatest advantage is its heavy weight and high maneuverability - two things that don't often go together. The weight keeps the car down on the ground and the maneuverability means it corners at high speeds and G-forces very well. This makes for great racing dynamics. Few cars can match that without getting into ridiculous price points. There's a rumor that Toyota plans to make an in-house small sport coupe to compete with the GT-R. Although not really comparable to the GT-R in its day, the Supra would be great to see making a comeback as a rear-drive sports car with more muscle than the GT86/FR-S, which itself is a fun little track driver. I got to put its twin, the Subaru BRZ, on the track this year and it was great.