12 speed vs Double Chainring + 5 speed

Hey guys, trying to weight up the pros and cons of of buying a 12 speed upgrade for my 4 speed or just get the 5 speed kit + a double chainring and tinker with it. I’m trying to chase more climbing ability (and maybe some top speed) as I’m working too hard to climb up hills (~6.5-10%).

I’m not a massive weight weenie so I’m not too concerned about the increased weight. I’ve already looked into the 7 speed and ATS/Schlumpf options as well.

Any feedback would be appreciated