Looking at the version of the Chieftain as shown on today's live stream, we seem to be getting a ship that has
- 430T hull, unless my math was wrong
- FAS core internals
- FAS optional internals with an extra size 4 mil slot instead of a regular size 3
- Slightly less raw firepower (~72 DPS with fixed pulses) than the FDL (~75), Python (~78), and Gunship (~82) but more than the FAS/Clipper (~60) and FDS (~66)
- Good (if unusual) hard point placement for using fixed weapons, with the larges being very close together
- 4 utility mounts (pretty standard)
- 504 hull (same as beluga) compared to the FDL (405), Python (468), Clipper (486), FDS/FAS (540) and Gunship (630)
- FAS Shields (but better, because lighter hull). Incidentally the Gunship gets similar shields when using a size 5 generator [noob]
- Excellent maneuverability (Max 44.08 pitch, 104.40 roll, 18.56 yaw, unengineered), outperforming the Python (34/104/12), FDS (35/93/16) and FDL (44/104/14), but looses out to the Gunship (29/93/21) and FAS (44/104/22) in yaw, and the Clipper (46/93/21) in both yaw and pitch
- Python speed (267 m/s) with better boost (Max 383 m/s unengineered), better than the Gunship and FDS, but looses out to the FAS in boost and is left choking on the dust from the FDL and Clipper
Overall, I would say that the Chieftain is comparable to the FAS. It has the same core internals (great for swapping between ships) can get the exact same hull with HRPs (unengineered), but has better DPS and hard point placement, better speed (23 m/s while not boosting), and due to the lighter hull has [slightly] better shields and jump range, all without the rank grind. However, it does lose out on yaw speed (~4 deg/s less) and some boost (23 m/s less) which are arguably the FAS's greatest advantages. It is worth noting that a combat fitted FAS is ~70T heavier than a Chieftain with the same build, and will not achieve its maximum performance since it is over 70T above its thruster's minimum mass, while the Chieftain is barely affected.
*Note that the stats I used are the maximum achievable without engineering, and will change based on loadout and engineering, and (in the case of the Chieftain) are subject to change by FDev*
Edit: Ninja'd by Alexander the Grape.