Jonny,
Have run none of those boxes so I cannot comment on them. I have been running the Smarty and its predecessor for 2 years. It gives a HUGE hand to the low/mid ranges of the rpm band and even helps out the upper end because of added timing and fuel. While towing a 20,000GVW camper up Monteagle in TN the Smarty/RV275 injectors keep me from slowing down at all until I need to for a curve and then the speed picks right back up if I so desire.
I doubt you will be disappointed by Smarty.
BTW, is your transmission stock or modded?
Godspeed,
Trent