Old sluggish Clara HD

I bought a refurbished Clara HD on eBay, really cheap. It is updated to the latest firmware and works perfectly fine, except for the speed. It is super slow to respond, which is not surprising given its age.

I'm considering doing a factory reset back to whatever original firmware it had. Is this a bad idea? Would it help? I suppose I would have to keep wifi off forever if I did?

Also, I use NickleMenu so that I have screen inversion available. Would I be able to make that happen with the older firmware?

I would appreciate any advice before I make a mess.