Riv advised so for a very good reason .... do heed it as they don't want unhappy customers anymore than you want to be one !
For the most part bikes for tall people not only need to to be taller but longer in overall reach from center, without the need for very tall/long reach stems and/or long(>25mm) setback seatposts. Save your cash for a custom as you can pay for it now, or buy some frames that don't fit and end up selling... amounting to more time/effort/angst/$$ than if you had just bought the custom one first of all.