If I were you and had to pull the trigger sight unseen: I'd go 52 and low-step. Take my opinion with a grain of salt as this is me translating my experience with the 4.0 Trekking 48 high step (and I'm an inch shorter than you). Might be completely revised/different geometry.
Your frame has a reach of 365mm in 48, right? These new frames are different to yours.
This model has a reach of 394mm in size 48 low-step. The advantage of the smaller 48 lo-step frame is that you can put a suspension device on the seatpost without worrying. The disadvantage is that the second MRS battery might not fit. The 52 lo-step has a head tube of 170mm and a stack of 666. That means that the 52 lo-step frame will be 2 cms higher than the 52 hi-step frame. This affects handlebar height and might place the handlebars higher depending on the number of spacers given. That could be good or bad, depending on the OP’s preferences.
The dealer said he would handle the size to the OP’s satisfaction. So he no longer needs to worry.
I first need to sell my current bike which is a huge challenge. It has 17,300 kilometres and has a slight wiggle in the drive. I don't want to misrepresent it to a potential buyer, so I won't be resetting the counter (as many people do). The bike has the miles that it has. However, it's almost unsellable. Most 2nd bikes in my locale have less than 3000 kilometers. But if I ever get to switch, it will be a size 52 lo-step. I'm 6ft0.