what do you consider 'measurable'? THe quest has about a 90 horizontal FOV. I think the Valve index does about 120, and the pimax headsets range from the Artisan at 140 horizontal through the 5 and 8 series at 170 horizontal. The Star VR1 does around 200 I think, but it's a limited sale item, and hasn't got great reviews from my acquaintances who have managed to get a hold of one. IF you can get one, it's about $3000.00 US.
I have a Pimax 8kx, and once you get it dialed in, it's pretty amazing. It's not cheap either. Unfortunately. The Artisan is a good bet at around $499 US and prices go up from there.
There are issues with wider FOV... it appears to be much harder to create a lens system that works right out of the box for most consumers. OTOH, even my old oculus rift took some tweaking. Further, for many games, it's really not needed and the Reverb G2 will do very well. For flight and driving sims tho', there's no substitute for wider FOV.
cheers
finnster