If you find yourself out of gear on long downhills and spinning out in a 46/11, then only option is to swap to a compact road crank that will get you a 50 big ring or a 39/53 crank. But that maybe yields 4 mph in the 53/11, so your call.
You can play with different cassette and crank options and find out speed here.
Mike Sherman's Bicycle Gear Calculator (mike-sherman.github.io)
You can also get a 2nd wheelset and put the road tires, maybe 28mm's on that with a road cassette like an 11-28. Then keep the gravel tires and hills gears on the original wheel set. On the carbon Topstone you would have to have a shop re-dish the rear wheel but that easy and cheap. A 2nd wheel set is what a lot of users of this bike do, it's how I have my aluminum Topstone setup, works great.
And FWIW, my experience is that my alu Topstone at 22 lbs with the road wheels on it, is about 5 lbs heavier and maybe 1/2 mph slower than my 17 lbs carbon road bike. I notice it on group rides.