Protools CPTK2 or Native for locking up to an external device

[s0und80y]

Hi crew,

I'm in the process of putting together a new post production rig/
I'm tossing up between a CPTK2 mbox pro rig or a Native PCIE.

Most of my work will be recording the mix and stems back into the box, however.
I may need to lock up my system to a a digi or HD rig, and also a fairlight in the future when doing film work.

If i'm slaving LTC and converting to midi with an mbox pro, what is the drift?
Is it reliable enough, when working with a Fairlight will it lock up fast enough?

Should I just stick with a native PCIE and a Sync i/o ???



Cheers

Mark