Expanding on what Necrosis said a bit:
The Repentia can't actually buy their own Rhino. While they can borrow one at the same cost from the Battle Sisters you listed, they then can't start out in it, so they're out in the open at game start, potentially opening them up to a turn of fire.
As the Rhinos aren't Assault Vehicles, the Repentia also can't get out and then declare a charge that same turn (well, not in 6th, anyway) so they'll likely be taking ANOTHER turn of fire, this time from close range.
At this point, you're better off walking. Which also has them open to enemy fire, so yeah, a couple editions and a laundry list of Special Rules further and Repentia STILL can't be made to work - short of an enemy that is kind enough to 'open' the nearby Rhino for you in his turn. Any battle plan that depends on the enemy doing you a favor probably shouldn't be relied upon.
Fast attack choices, Dominions with the Scouts rule and Holy Fusillade AoF are generally better than the Elite section's Celestians (and cheaper, too).
The other FA unit is Seraphim. Mobility is fantastic, and I've yet to meet something whose day can't be ruined by four Inferno Pistols. Outfitting them with Hand Flamers works wonders on infantry blobs. They also make a great bodyguard for Celestine (but know when to leave her to fend for herself
). I'd recommend bringing a squad with Inferno Pistols, because your current list badly needs some more anti-vehicle. Yes, they're less powerful in 6th and there tend to be less around, but right now you plain CAN'T deal with any high-AV that rumbles onto the table.
Extra Armour on Exorcists is mostly useless - you want to keep them shooting far more than you want to keep them moving, and whether the crew is Shaken or Stunned they can only fire Snap Shots either way.
Stepping outside of what Necrosis already discussed:
For the Battle Conclave, while I can see why you'd want Power Axes, the models come with swords
(and they're metal... )
For the normal Sisters, I'd take another look at squad sizes and weapon loadout. If you've got 10, they'll fit in a Rhino so they can get to objectives faster and safer. If you're going for a large unit that'll be hellishly difficult to shift in shooting, you might as well go all the way and grab 20.
Assuming you've already considered that, think on ditching the flamers on one squad for Meltaguns. Flamers can't handle every situation. Meltaguns can, and you've got enough bolters in a squad that you're not helpless against infantry anyway