Originally Posted by chxf

All SRT6 have a limiter. The normal XF don't. And the mexicancrossfire has a normal one. See this older post. So if you pimp a normal XF, it hits higher speed than a SRT6.
But I doubt that with chip and catback 168 mph can be achieved. There must be more HP involved...

@ABlueSRT6: There shouldn't be any vibrations at 140 mph not at 150 mph. I often do top speed. The XF is like on guide rail. The only negative effect is wind noise ... and higher pulse.