I haven' t shot the Thunderheads but I have shot plenty of Spitfires . I personally prefer the Pro series . It' s only a couple $ more . I' m not sure either whether the grooves in the ferrule make a very noticable difference in arrow flight or penetration, but I will say the finish on the ferrule and nickel plated tip on the pro-series is much better than the regulars . My used regular Spitfires are scratched all up and the tips have rusted (they look very used), my used Pro-series Spitfires have all taken multiple deer/varmits and all still look brand new . JMHO .....but I think that' s worth the $2-3 a pack .