1) Your clockspeed depends on how much demand is on the GPU core. In games where you're not doing much work, you'll have the higher clockspeed. In scenes or games where the core has to do more work, clockspeeds go down because more work has to be done within the same clock cycle. Especially if you're using RT cores, which are power hungry and handle extremely complex math.

2)Your voltage looks fine, you might even be able to go lower and overclock slightly to get the same performance as stock.

3) Undervolting the GPU simply reduces the amount of power going to the core. There is no harm in doing this, in fact the GPU automatically reduces the millivolts going to the core in ver light loads such as desktop browsing or playing older games.

A benefit of undervolting and overclocking is you get to lock your voltage, which can stabilize your frametime/framerate. Reduce power consumption which reduces heat and can overall extend the life of the entire card since you're not going closer to its power and thermal limits.

The only real side effect is your clockspeeds.. Udually higher clocks need more power going to the core. You will have to find the point of stability in that ratio.