I took a little different approach that you may want to consider - or not
I’ve got 28c tubeless road tires on 3T Discus C45s that I take on minor gravel on my 3T Strada. If I want to go faster on and off road, I’ll swap those 700c wheels onto my Exploro with tires that have some tread. Later this year for CX racing and BWR (if they happen - next year if they don’t) I’ll put some Serac CX Sand Tubeless tires on them.
I don’t plan on doing any gravel racing in 2020, just training rides and hopefully some rides with friends. The 650b wheels on the Exploro with 2.0 Ventures spec out to the same circumference as the 700c wheels and tires, so, handling stays the same, just a tire with more volume and comfort.
So, a similar strategy would be: you already have a set of 700c wheels, and any “upgrade” will yield marginal gains - which, again. won’t matter unless you’re racing. Having a set of 700c and 650b wheels with big tires will give you more comfort and speed depending on where you’re going. The 3T DiscusPlus i28 LTD wheels are amazing.
If you don’t what to go that route, and want to stick to 700c wheels, the 3T Discus C45s are designed to be the fastest wheel with with wide tires. For Gravel racing, those wheels and the IRC Boken in 700c x 40c would be super fast.
Disclaimer. I’m very partial to 3T because that’s our team bike, but it’s our team bike because we’re so in love with 3T products (not all of us ride 3T).