What is worse for a engine big or small turbo

What would be safer to run small turbo high boost 2bar+ or big turbo low boost to produce the same horsepower i.e 800 bhp

Or would it be the same thing?

The more power you can make at lower boost is better, however there are so many other factors to consider including the driving experience of them both

Doesn't this depend on spec and how much lag you want it to have/not have?

Depends on power level, then find the smallest turbo capable of that power safely I would have thought.

more boost = more heat so you would need to consider a cooling system upgrade.

Also change your name to v161. It has better Synchros and gearing..

Precision 6766 .81 A/R = Job done!

small turbo would produce a lot more torque so would be more strain on the engine

Simplistically put, boost is boost. BUT, you also need to factor in that a bigger turbo, producing the required air flow at a lower turbine shaft speed may heat the air less than a small one running at the edge of its efficiency curve, and thrashing the air. Plus you have to factor in how much lag you are willing to put up with, (lots if you want a genuine 800 BHP from a road car 3 litre engine). If the engine simply had to make 800 BHP at a fixed rpm and load, as in a generator, or to some extent, in an aircraft or ship, you would choose a turbo that gave the required air flow in the very best part of its efficiency range. The fact a road car engine operates over its full RPM range, and is expected to be pretty well mannered with some semblance of a sensible torque curve makes compromises essential.

I tend to lose interest when 800 BHP + is mooted, as I know with a single turbo, genuine power figures of that level from a 2JZ will translate to being awful on the road, with lots of lag, huge fuel consumption, with the need for frequent rebuilds, (if it lasts long at all). 800 BHP from 3 litres is race engine power, with acceptance of all the compromises and consequences running such a beast brings.