Maru, you should definitely go with X flex.
My swing speed is about that of yours and I'd tried both the S and X flex with my TP driver.
While Speeder757S is great, you'll find that the X flex is even better for you. I'm not losing any distance with the X flex at all and I think it's much straighter. Beside, the weight difference is only 4 grams I think. You'll hardly feel any additional weight with the X. You're right on the border between S and X, I'd definelty go with the X flex.
BTW does anybody know if there's a difference between the TM speeder 757 on TP driver and the regular Fujikura Speeder757?
Also, the difference between Speeder 757 and Speeder 757 Tour-Spec beside the cosmetic?