I have both:

Ball specs:
X-Factor 1500 grit polished, 3-3.5 pin, pin just right of ring at 2:00, 4" pin to PAP, RAD in strong position
Flash Point 1500 grit polished, 2-2.5 pin, pin just below fingers on bridge line, 5" pin to PAP, MB in strong position

X-Factor can handle more oil, has good length with a strong flip in the backend, I can use it from Med/Lt to Med/Hvy.
The Flash Point has about the same length, with a smooth controlled arc, I can use it from Med/Lt to Med.
Basically the X-Factor is about 3-4 boards stronger.

For me they compliment each other very well.

I would tend to recommend the Flash Point since you say you prefer to play the up and in shot because in my experience most houses just don't have enough oil outside for the X and it is a bit over/under for me if it hits dry to early. For instance when I first got the Flash and I was still in the comparison stages I threw several balls with the Flash were I was playing a swing shot where I was setting down on 13, 10 at arrows, 7 around 30' and it was hitting the pocket like it had eyes, I tried 4 shots with the X using the same line results were 2 brooklyns and 2 burn-ups that never turned.

Hope this helps.
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STORMIN1