Not quite. Say we use Duchess as an example, who has a base speed of 103. Also, for simplicity, let's say we use one Speed set, with the remaining items coming from other places, and let's assume you go Red/Blue and take Lore of Steel. Let's also assume that each of the six items that can have a speed substat do, in fact, have one. Finally, let's assume you have an average of a double speed roll on each of those speed substats, and that your glyphs give an average of +4 speed.
BaseSpd = 103
SetBonus = 0.12*1.15*103 = 14
SpeedBoots = 45
SpeedSubstat = (6 + 5.5*2 + 4)*6 = 126
TotalSpeed = 103 + 14 + 45 + 126 = 288
That's not really a tall order to reach, and it even offers you with a bit of leeway to not require double substat rolls on each item. You can afford to only hit speed once on three of your six items, and still reach 260 speed.