The 6.0 is by far the lesser evil. The 6.4 has all the same issues as the 6.0 (its basically the same engine) with more emissions junk hanging off it to fail and cause problems, and it has a more complicated turbo system to fail and cause problems.
Regarding the EGR delete, the only state I've ever heard of having an issue with it is CA. In CA they do a visual inspection under the hood and the inspectors know what they are looking for. Emissions vary state to state. Many states have no emissions testing for vehicles over 8600lbs GVWR. Even if they test emissions the EGR not working won't matter as it does nothing at idle. The only concern is visual inspection, and you really have to look to tell if the cooler is there or not, and most importantly you have to know what you are looking at. Technically emissions are a Federal standard, but since the Federal government doesn't want to spend any money on enforcement they have left it up to the states to run their own emissions testing programs. I'm all for clean air, but if you know how the EGR works you realize that it is in operation almost never, and it can potentially destroy an engine. To my mind its unfair that the end user has been saddled with this. To each his own, but mine is gone.
Regarding head studs. They are mandatory if you want to prevent a failure. Tuning may exacerbate the issue, but the underlying issue is a design flaw that allows the heads to lose their clamp load on the block over time, allowing the gaskets to seep under load. There are only 10 bolts holding each head on the 6.0. The same as a small block Ford, the same as a GM LS series engines. Those gas engines have head gasket issues when people put forced induction on them, and those as gas engines running maybe 7-11psi of boost. Diesels make a lot more cylinder pressure because there is more energy in Diesel fuel, and then you are putting near 30psi on top of that. If IH had used studs maybe it would have been okay, but instead they used Torque To Yield bolts to make assembly line production easier. Those bolts are installed in a state where they are in essence partially failed already. This is why they cannot be reused. I'm not going to get into a metallurgical discussion here, but the bottom line is that after so many cycles the bolts fatigue and fail to spring back when loaded and bye, bye head gasket. There's no set amount of time this will take. I've seen them blow at 40k miles; I've seen it take 220k. But fail they eventually will.
Should you buy a 6.0 truck? Personally I think yes, because the irrational fear people have of these engines has ensured they sell cheap. You need to buy it knowing that to make it truly reliable you may need to sink another $5-$6k into it. But from '03 onwards there's nothing else I can recommend that has the capabilities of a 6.0 truck that is going to be any better. The newer Diesels are just much more complicated that the old ones and you're never going to get that same level of inherent reliability from something that has twice as many parts. Emissions and the quest for power has mandated electronic engine controls, etc. But its not all bad. The SD series of trucks is a great platform. Its tough and truly heavy duty, not just a 1/2 ton with a bigger engine and axles as they used to be. The transmission is awesome in these trucks. They have good brakes. They have a lot more comfortable interior. As a two rig they are great.
On the V10, pass. Basically they make no power AND get bad gas mileage. Not a good combination in my book. They also sometimes shoot spark plugs across the engine compartment just for fun like all the modular engines.
'06 F250 4x4 - 5" Flo Pro exhaust, SB Filter intake, Accufab elbow, Edge Evolution (monitoring only), SCT w/ ID custom tune, FASS 195 pump, Gillette Diesel EGR cooler delete, Sinister Diesel coolant filter, ELC coolant, updated turbo drain tube/oil feed line/STC fitting/oil cooler, ARPs w/OEM HGs, Elite coolant lines, ITP RR fuel system, RCD 175/30 injectors, Powermax, BD CCV, FICM.com FICM w/ ID tune, Elite UP, BPD water pump - 13.069 @ 101.94
'02 WRX - Outback rear disc swap, EBC green pads, DBA pillar vane rotors, TXS UP/TBE/TMIC, Perrin LW crank pulley, PPG billet steel shift forks, ACT Streetlite flywheel & clutch, K&N filter, STi Group N motor/trans mounts, TiC/Kartboy rear diff mounts/subframe lock bolts/outrigger stiffeners, Kartboy SS & all shifter bushings, custom PDX tune for Cobb AP - went 14.1 on a terrible 60ft before most of these mods; shooting for 13.50s