N.Y., it's mostly a matter of the added weight on the wider tires that becomes a factor, but the difference between a 25 and a 28 or 32 is pretty minimal and you can easily compensate for this by choosing a lighter model of tire. Better yet, if you go tubeless, you can actually reduce weight with a 32 if you are now running tubes in the narrower tires. I go tubeless on all my bikes, now.

Assuming equal weight and roughly similar rolling resistance, a wider tire can actually increase your speed, since going wider also means going taller on your wheel diameter. If you're looking at gravel bikes with those 700x35 class tires, tread design is going to be a big factor. If you plan to ride a lot of pavement, don't get too aggressive on the tread.

Back when I was riding drop bar road bikes, my average speed riding on pavement did not change much, if at all, between my carbon Domane with 700x28s and my Salsa Warbird (great gravel bike) aluminum with 700x35s. Can't remember the exact tires I had on the Warbird, but they were fairly smooth in the center with a row of knobs on the sides that didn't touch the pavement unless I went into a low turn. When I went into sand, though, those side lugs made a huge difference. I could ride the Warbird in sand and loose stuff whereas I absolutely could not ride the Domane with its usual road slicks in loose stuff. What I loved about the Warbird, most, though, was that it was noticeably more comfortable to ride on rough pavement and probably safer, too, with those wider tires. Don't miss the Domane at all, but I do miss that Warbird. It was a very capable bike.