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Are you saying that snow necessitates a fat bike?
IMO unless you live somewhere that it snows considerably more often that once or twice a year or, conversely, in the desert, fat bikes are an affectation and @plxarc will either enjoy that affectation and find little use for the 29er wheels or won't and will find little use for the fat wheels.
The weather and terrain to be ridden are unlikely to make the bike unrideable or even less enjoyable whichever set of wheels are fitted.
Are you in the UK?
We don't really have conditions that require fat bikes so I'd expect you'll either like the slower bouncier ride from the fat wheels and the 29er wheels will sit unused or vice versa.