I don't have a 4K PJ, but just upgraded to a faux-K projector and am using an anamorphic lens (Panamorph UH480). It is incredibly crisp. You don't need to spend 7000 bucks on a lens. Scour the classifieds here as well as Ebay. I've seen Isco III lenses go for as cheap as 2K, and my lens was recently listed for less than a grand. Crazy really. I tried zooming for my 2.35:1 screen and preferred using the lens. Honest answer...if you can get a lens cheap enough, I think you'll be very happy. Otherwise, get a projector with zoom and lens memory and I'm sure you'll also be very happy with that solution.
Gear: The Brains: Anthem MRX 720. The Brawn: Outlaw 7700. The Fun: Custom PC w/ Logitech 27 & reverse mount pedals, Nintendo Switch, Playstation PS4 Pro. The Visuals: Panny UB420, Epson 6040UB, Panamorph UH480, DIY 138" Curved screen using Semour Centerstage XD AT material. The Audio: 7.1.4: LCR: Tannoy DC12i. Sides: Tannoy IW63DC. Rears: Tannoy DC8i. Ceilings: Tannoy CMS 603/601 DCBM. Subs: 3X Micro Marty and 1X Full Marty.