"Buy the best servos you can afford" is Tom's advice and most other giant scale modelers.. I use 5645 digi's, and though they are not top of the line they do a great job for me.. Digitals are like servos on steroids IMO, they center much quicker and are more accurate.. If you go 6v use NIMH's and get the most out of your servos.. Unless you are going the LiPo route like many then use 7.4v and a regulator to step down the voltage.. Just wait, many will chime in and give their advice, and maybe someone is using the servos you mentioned..