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Well, there's a few points to make here.
First is about engines failing. Most engines are taken out by bad fuel, bad injectors, or a faulty tune. Built engines taken out by improper assembly usually fail within the first 50 miles. Whether it's built or stock, you have a much higher chance of killing it if you don't make sure your fuel, timing, and injectors are always on point.
Second is about engine limits. It really comes down to torque and how soon you want to make it, because this is really what determines cylinder pressure. A EFR6258 on an SR making 400wtq at 3500rpm is way harder on the engine than a 3076 that only makes 350wtq at 6000rpm even thought it will make bigger horsepower numbers. You have to take this into account when you talk about the limits of the pistons and rods.
Thirdly, piston cylinder-to-wall is only one clearance. You can offset this by using something like Mahle forged 4032 pistons with high silicon content. This allows you to run tighter piston to wall and have that OEM like startup-and-go kind of engine but still have stronger than stock pistons. This can also reduce cylinder wall wear compared to a big power 2618 setup with big cylinder-to-wall.
Bearing clearances should be opened up on almost any engine you're going to beat on or make more power on. This should be accompanied with an appropriate increase in oil viscosity. SR20 blocks are not very stiff and move around quite a bit, and factory tolerances are just not up to snuff when the engine is wrung out. I think this is the main mistake people make when building SR's and making power.
Now you can see that there is a lot of minutia in making the choice between built and stock. Depending on turbo choice, I would say going with Mahle pistons and stock rods, opening up the bearing clearances, and doing the dual rocker guide mod would leave you with a very reliable engine as long as you weren't trying to make too much torque.
As an example, I have a EFR 6258, and I elected to put forged rods and 2618 pistons in so I can let that thing eat as much air as it can at low rpm and make the two liter drive like a five liter. I also plan to beat the living daylights out of it, and would like as much margin as possible when it comes to detonation. I probably could have gone with a high silicon piston and been fine though.
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