The X53 actually comes with a better 15 mm fan than the Noctua, its just that the Noctua sound profile is nicer. In terms of performance, the supplied 92 x 15 mm fan is even beating out most regular sized 92 x 25 mm fans.
Other option: X47 Full Copper + 25 mm fan + Silversoul 110.
The SS 110 supplies you with TWO important things:
1. Best regularly available 92 x 25 pwm fan (in terms of cooling performance, not noise) and ..
2. A set of 25 mm fan brackets that fit any 92 mm Thermalright CPU cooler - eg. if you dont want to use the before-mentioned 25 mm fan, but a different brand; its actually TWO sets, so you could still use the SS 110 in a different build, too
Yes. thats about the only way - except maybe asking the Thermalright support nicely - to get ahold of those parts. So if you've wondered where reviewers / testers got these - they had them still sitting around from a test of the SS 110
And X47, because: What I read so far is, that in terms of performance, the X47 and X53 FULL Copper are almost identical. And if you have like 60 mm to spare, you can still go with a 25 mm fan (57 + 3 mm distance to avoid the noise issue with the Terra side panels; maybe optimize with the Noctua NA-FD1 foam set).
cu, w0lf.
ps: Beware if you pick a Gigabyte board - their sockets are 1 - 2 mm higher than the rest. So in that case, a X47 (full copper) is a must have.