It could be accurate. Drivability is a funny thing, and with the cable operated systems the ECM looked at the throttleplate position (using a TPS) to determine how much extra fuel to dump in to improve tip-in response. It worked alot like the accelerator pump on a carburetor.
With drive-by-wire control, the ECM controls the rate of opening directly, so it doesn't need a sensor to tell it where the throttleplate is, it already knows because it is controlling it directly. This means the fuel dump for tip-in can be better matched to the engine's needs.
It doesn't mean the factory settings are optimized for hard use though. They are optimized to give most reliable operation under a wide range of conditions. If you narrow down that range of conditions and go a little closer to ideal, you may find better response. I suspect that's what your friends are commenting about.
Red line starts as a function of mean piston speed. 20 meters/sec is the generally acknowledged acceptable speed for durability. The 2AZ hits 20 m/sec at exactly 6250 rpm; coincidentally our base red line is at 6250. If you are willing to accept shorter service life, you can spin up to 7630 rpm for the same 24.4 m/sec mean piston speed as a Type R Integra (the highest mean piston speed of any street production engine including Honda's NSX).
The real question about raising the redline is what is in it for me if I do? There are three big questions that go along with this:
1. Does the cylinder head flow enough to support raising the redline?
2. Do the cams (and valve springs) support raising the redline?
3. Do the intake and exhaust support raising the redline?
If the ports and valves in the head will continue to flow more air without the airflow going supersonic at higher rpm, then we've answered #1.
If the cam profiles have already been maximized to work with the bottom end geometry (rod length to stroke ratio) and the valves and springs don't float or oscillate at the raised redline, we've answered #2.
If the intake (all the way from where the air goes in the opening to the cylinder head's opening) and the exhaust (from where the exhaust port meets the header to the tip of the tailpipe) support the increased flow from raising the redline, then we've answered #3.
If we have a thumbs up on all three questions, we will make more torque at higher rpm, and therefore, more power. Ideally we make the same torque from the bottom of where we want the engine to be strong, all the way to redline, although usually torque starts to drop off before we get to redline.
A turbo, or any other kind of forced induction, will try to make more air move through the same system. Raising the intake pressure is always helpful, but again, you need to have the entire intake all the way to the valve seat correctly sized and the exhaust all the way from the valve seat correctly sized to take full advantage of forced induction.
Sure, you can slap on a pressure inducing device and get more, but if you really want to see the improvements, especially at high rpm, you'll need to take the head off and make some pretty radical changes to it to let more air into the cylinder. I've done this for an NA Supra head, and the port size difference between the stock GTE head and the stock NA head is huge. Basically just think of adding 4mm diameter to the entire port on the intake side. That's a LOT in the porting business.
So, if I took off the head and added some size to the ports and probably the valves too, we'd get more flow. More flow means more power at the high end of the rpm range which is where we planned to go anyway, so it's all good, assuming the rest of the intake and exhaust are up to the task. Without modifying the ports or without changing the cam profiles, you are correct; more rpm won't get you a whole lot.
Last but not least, you also have to pick your FI device to match your desired rpm range. A big turbo (like a T-61 for our cars) will give great boost at high rpm (because it needs a lot of waste heat to drive it and we don't start making lots of waste heat until we really get the rpm up), but may not be too fun around town for stoplight racing.
Here again, we have to decide what rpm range we want to be responsive and pick our components to match that range. Too big is just as bad as too small. Lots of would-be porting guys find this out the first time they do a head. They almost always make the ports too big and the engine builder suffers as much embarrassment as the driver does.
Your question about a turbo is pretty easy to answer: no matter what, the engine will make more power under boost, but it won't fix the problems you need to solve to make more power above redline all by itself.
