All these numbers flying around are giving me a headache.
There is not necessarily any correlation between what one manufacturer calls a '59cm' and what another manufacturer calls a '59cm.' There are different styles of frame (traditional vs. sloping/compact for example), different measuring techniques (c-c, c-t, virtual c-c), and these are only talking about the seat tube length... a different manufacturer or even a different model from the same manufacturer will have different top-tube length and different head tube lengths as well as different head and seat angles, stem lengths, seatpost setbacks, bottom bracket drops, etc, which all affect the fit.
There are two ways to determine if a bike is right for you - measure an existing bike you know is comfortable for you and compare to the one you are considering buying, or try the bike out.
In general, though, if Novara is calling their 59cm an 'XL' size, then it is likely a sloping top tube, which means it likely fits like a traditional level-top-tube bike of 3 or 4 cm more - like a 62 or 63 or so. If you fit well on a 58cm level top tube LHT, then a 59cm sloping top tube bike will probably feel pretty big.