This:
https://www.youtube.com/watch?... ... video includes a performance review of the VisionFive 2 board, which uses the same processor as the Star64.
Summary: If you are looking for performance, stick with ARM. This chip is not yet competitive with latest ARM designs. RiscV is still new and will take a while to evolve. Given ARM's huge head start, RiscV may never catch up. So again, if you're strictly concerned with performance, skip this and stay with ARM.
Having said that, are you aware that ARM just announced that they are changing their license model so that their royalty per CPU will be based on the cost of the device it is used in, rather than a straight "per CPU ARM license?" I doubt this will make a big change to SBC prices, as they are quite affordable. I think it's aimed more at the premium smartphone market, where ARM wants a bigger "piece of the action". This is part of ARM's ambition to go public soon.
My interest in this board is that RiscV is an open instruction set (which is not the same as open source, but still more free than fully proprietary), and most importantly - DUAL GIGABIT ETHERNETS AT A MODEST PRICE! I have been waiting years for a board like this.