Best leadscrews for i3??

Hi all,
im looking to upgrade my i3 from standard m5 threaded to proper leadscrews but im having trouble finding which ones to use that will fit the X Ends and a supplier that doesnt charge a fortune for them ideally in the UK but anywhere will do. I'm also not sure whether or not to just get the leadscrew and use a flexible coupler to attach it or to get the motor with a built in leadscrew shaft, im not sure if there would be any benefit of choosing one over the other?

Does anyone know which i should get and which suppliers are good? is anyone currently using proper leadscrews on their i3? have they improved the print quality?

Kind regards

I am also looking into upgrading My i3 to leadscrews in an effort to get rid of z-banding.

Has anyone got much experience of using them on an i3, and do they justify the price over el-cheapo 5mm threaded rod? I don't mind spending the money if they make a difference.

Would standard Acme/trapezoidal be a safer bet than something like Eichenberger high-helix?

Cheers.