I'm a big fan of GP 5000 S TR tubeless. I'd go with the widest tire you can fit. Of course make sure it is appropriate for your rim width.

If that's a 32, go for it. I recently put on 32 mm after wearing out my 28's on my Domane. It's every bit as fast as it was on the 28's and maybe even faster. I'm riding at 18-20 MPH. If I were able to ride significantly faster, maybe the aero losses of the 32 mm being wider would hurt. But at this point, I plan to stick with 32 mm from here on out.

Just going from the Bontrager R3 to GP 5000 tubed, you're still likely looking at 10 W or more of savings. That's a huge difference. The GP 5000 are arguably the best road tire out there. I'm not sure there is a good Bontrager tire.

Depending how fast you ride, you might expect ~0.5 MPH increase in speed with the same effort.

The GP 5000's are more expensive. But you took ~3 years to put on 4k miles, so you're going to get years out of them and the cost per year is pretty low. My experience with the GP 5000 S TR is they wear VERY well, are as good or better at puncture protection then other tires I've used. They DO NOT wear fast and they DO NOT puncture easily. Are there tires that wear less or have more puncture protection? I'm sure there are, but the GP 5000's are very good in this regard. They are not a fragile or delicate tire.