What is the best 140mm case fan if money's no object?
There isn't any (any 140mm fan has its drawbacks): the Fractal Design GP-14 are appropriate, so just listen to them, and if you please them, then stick with them.
there is some desire to match all the fans in the system and end up having 3x noctua a15's on the case and 1x a15 on the cpu cooler. Are the gp-14's up to par with noctua or some 1 else?
Often aesthetical desires don't match well functional requirements (set aside matching style and colours is also an expensive quest): YMMV.
The Noctua NF-A15 has a better build quality than the Fractal stock fans and it can be dialed down by PWM to a very lower pace, but tonally they are not preferable to the GP-14: besides it's 150mm wide, so I'm not sure it may work on the case mountings without issue (but you might just check that out with your one); OTOH the Fractal GP-14 is not well suited to work on an heatsink, they are also a tad slower (1000rpm vs 1500rpm, so they might be even less effective on the most heavy loads), and moreover it isn't a PWM fan, so that not all the motherboards may drive it by the CPU fan header.