Reply to "Atomic EFI vs. FAST EZ-EFI 2.0"

I have been running an MSD Atomic FI for about 9 months now and I am pretty pleased about the results. I have no experience of other 3rd party EFI systems so I cannot compare results.
The Atomic is controlling timing and running a return fuel system with regulator, I would recommend you strongly consider both options for drivability and reliability. Some Atomic users complained of low speed stumble until they went to a return system, prevents hot-soak issues, etc. With timing control no more messing with springs, stops or moving vac hookup or amount.
My engine is a 393ci with a 248/252 @ 0.050 mechanical roller camshaft with 626 crank hp, so I am at the limit at what the Atomic recommends.
My cold and warm starts are great, idle is really good, I get ~16mpg on a run, no issues with reliability, acceleration is fantastic.
The one issue I do have is a slight bucking when driving at low rpm. At less than about 2,000rpm on a constant throttle, the car feels like it is missing and you feel the car jerking a bit, not violent. Anything less than ~40mph in 5th requires a lower gear. I have tried different settings which have made it better but it might just be a characteristic of my aggressive cam and getting reversion. Atomic are working on an update which is supposed to be coming out soon and will give that a try. If parts fail, i.e. o2 sensor, idle control etc, generic parts are available but if you want them covered under warranty you need to send the complete unit in to MSD.
The ability to change timing, vac advance, pump squirt etc while driving via the little handset is great, you also get a nice accurate reading of your water temp..
When Kuntz & co dyno'd my engine they also put on the Atomic with my old Hall Pantera GTS headers, 552hp @ 6,200rpm, 505lb-ft @ 4,800rpm, instead of 626hp @ 6,700rpm, 556lb-ft @ 4,900rpm with dyno carb & headers, quite a drop. Kuntz were not familiar with the Atomic so the stock Atomic fuel pump I sent them would not have been big enough so maybe some setup issues, rotor phasing etc. Now running a high hp pump return system with Pat Mical's headers and my butt dyno is happy.