Honest question - you shoot 720p to tape?
Only if you don't want to round trip. If you want a one-way street, watch Hunter's video
Wouldn't be real life if someone wasn't smoking, m'I right? :)
According to IMDb, Public Enemies was shot on/with the following:
Arriflex 235, Cooke S4 Lenses
Arriflex 435, Cooke S4 Lenses
Sony CineAlta F23, Zeiss DigiPrime and Fujinon E-Series Lenses
Sony CineAlta HDC-F950, Zeiss DigiPrime and Fujinon E-Series Lenses
I would say probably after the onlining so that your picture lock dictates your VFX needs, but if your pre-planning is exact enough you could conceivably do VFX work alongside the editing process. You'd just need better-than-proxy quality plates for the shots to be VFX'd. Let me know what you end up doing!