Whats your swingspeed mine was 115mph last time i was on a swing moniter they told me i needed a regular True Temper gold shaft,Which they happened to have in stock.
115 would be borderline for an X-Stiff tour shaft.
At 115 they were downright trying to con you by saying you were regular as 95 would be the border to think about going from R300 to S300 in the dynamic gold shaft.
My swing speed was between 105-120 mph, I can hit tour spec shafts if I swing it hard but get no consistency.
Anyhow, you were advised really badly but at 115, the Project-X 5.5 or even 6.0 Will be fine for you.
I would favour the 5.5 as you wont have to work it as hard.