I'd reply for both @Pigdog and @hazzer19
Thanks!
Based on my direct observation, this frame could actually accept 700x35c, but I could be wrong. Someone mentioned in this thread that they successfully fitted 700x34c Schwalbe slick with some space still.
I decided to get a set of 650b wheels in attempt to clear the toe overlap. On gravel, toe overlap is something I don't want to experience. With 650x35b, it successfully cleared the toe overlap; 700x35c will definitely make it worse.
Is there any space left with 650x35b? Yes. Around 1.5mm to the drive-side chain stay. So, in theory, you could jam in a set of 37mm, if you can find any. But better not. 35mm is the widest you can fit safely. 40mm is definitely a big no.
How it rides on gravel? I haven't actually test it on real gravel yet. Also, they are tubed for now due to Hunt's rim tapes came in a such poor condition. That means that I won't be able to enjoy the full experience even if I ride it on real gravel.