Only way to go is with the custom tune. I would never run a tuning box or generic tune on this engine. You bought a premium engine, don't put cheap tuners on it. I run the Custom Spooling tune with DPF and EGR delete. Its the best tune out there. I have posted my 1/4 mile runs which I think the only other person to run a CRD in the 1/4 was from Australia and posted. Its extremely quick with almost zero lag. I also removed the turbo resonator, welded up a 3" aluminum turbo intake tube, and installed a devil's own methanol injection system. I have talked with that guy on the mbworld forum numerous times. I will probably get one of those turbos from him. There are some other guys running larger turbos on these engines, but they are in Finland and don't post on English sites. There really isn't much bolt on, but I am working on a few things. The most important mods are elephant mod to remove CCV gases, swirl motor 4.7K resistor mod, turbo resonator removal, dpf and egr delete tuning. Anymore power than that and you will need transmission upgrades. All the good current tunes reduce power in 1 & 2 gear to keep the transmission alive. I will be getting a Paramount transmission in the future to handle the power.
2014 WK2 EcoDiesel LTD, Trail Rated, GDE tune, Offroad Exhaust, 275/70/18 Duratracs
2008 WK CRD LTD - GDE ECO Tune, 3" Intercooler, CBE exhaust, GTB2260VKLR, 3.07 gears
2007 WK CRD LTD - Max output, GTB2265VKLR, Long travel, wilwood brake 6 piston front 4 rear