People seem to get hung up on not being fit enough for single speed, its like anything, if you stick with it past the initial rides ,you soon learn the simplicity of Single speeding.
I ride Fs, Hardtails, Retro ,geared and single speed . I do love the simple life of single speeding, low maintenance – just brakes and chain , the featherlight weight – I enjoy thrashing it around and climbs.
Climbs that are too steep to ride, I can push the lightweight bike up quicker than it can be ridden in the granny gear.
you can build a single speed very cheaply if you want to try it before spending a decent amount on one .
I run 34T x 18 which XC is ideal for me