The input max is for most inverters on the market now a setpoint where they will simply disconnect, stop generating power and go into an error state that you need to hard-reset if you want to use the inverter again. It's pretty typical to have a 1000V hard limit on a nominally 800V or 600V system. If you're going to ride close to the limit then on some days you will see overvoltage and disconnects. So it is something you simply should not do. But people think that if the label says 1000V then 990V total nominal panel voltage should be fine, which it obviously is not. Panels are analog devices, they will produce an open circuit voltage much higher than their nominal use voltage and when you're on a switched mode inverter that means that the average voltage may well be 'in spec' but the voltage from one millisecond to another may well be outside of that if the system was built 'on the edge'. And because inverters have to take the grid side into account as well (they are not allowed to exceed certain voltages) there is always the risk of not being able to load the panels sufficiently to get the voltage to drop. So you should side your system so that the open loop voltage of your panels under ideal conditions is still comfortably lower than the max input voltage of the inverter. 800V nominal is pretty close to that limit, 700 is better and 600 is playing it safe.

I think one of the main reasons why installers tend to overprovision voltage wise is that they count on the inverters switching off the whole string every now and then versus being able to make more power without a lot of additional wiring under normal conditions. The net effect of that is positive.

Low quality inverters (the ones without the ability to disconnect the HV side autonomously) should be avoided like the plague anyway, those are simply unsafe and as far as I am concerned should not be allowed for re-sale at all.

My own system can make 17KW on a very good day in March at 1 pm or so, but normally it is closer to 12KW even in the summer. So those peaks are actually substantially over the normal output. Over a given day the average is about 5 KW or so from sunrise to sundown, and those first and last hours hardly contribute.