I really depends on your set up. Most modern bows today can produce enough energy (even with shorter draws) so that you can use mechanical heads with easy pass throughs.As far as the Spitfires, I have used them (two and three blade 100's) as well as fixed heads (Thunderhead 100's).I have found no difference in the two as far as penetration goes but it seems (to me at least) the mechanicals tend to produce more damage andmore blood loss than thefixed heads.

I will probably end up using mechanical heads all year this year, and only Spitfires. They have never let me down in either their function or performance. What else can you ask for?