Individual differences have a greater effect on performance than Java vs. C/C++ .. up to 30x performance ratio between the median programs of the upper and lower half... up to 20x differences in programming time for experienced graduate students.
-- Prechelt, L., "Comparing Java vs. C/C++ efficiency differences to interpersonal differences", Communications of the ACM, v42, 10, October 1999, pp. 109-112.