Either one is safe IF, and I say IF, they are tuned correctly...you MUST get them tuned by someone who knows what they are doing...also, the amount of boost they are making will determine whether or not the stock engine will support them or not...
When dealing with any type of power adder (i.e. tubro, nitrous
, s/c, etc), everything depends on the tune...if the tune is done badly, then the motor goes boom...if it is tuned correctly, you should have a long lasting, high performing engine, depending on how much boost you are wanting to run or power you want to make...
'05 GT - Borla Catback, JLT Series 3 Intake & SCT SF3 Tuner, Koni Adjustable Shocks/Struts, H&R Race Springs, Roush Shifter, Hawk HP+ Brakes all around, Steeda Front Sway Bar & End-Links, Royal Purple Fluids
'2011 F-250 Super Duty Crew Cab - 6.7L PSD 4x4