I have been stringing for a few years and string probably 100 rackets a year on a crank/lockout machine. I am looking to upgraded to a nicer, newer electronic machine. I have narrowed it down to these three: Gamma 7900 els, Alpha Ghost 2, and Tourna 700 ES. I am also open to other suggestions but would like to keep it in the 2.5k-3k prince range. Also, do I need a machine with self-centering, or is it over-rated? Any advice on which machine I should choose?