I know the 56 series servos get some bad rap around here. I have used them and the 5625's for quite a while with great luck. I have had one bad one that showed up right away during setup. Got about 75 flights on my P-70 powered Roo this year with 4 5625' on the primary surfaces and they worked perfectly and centered great. (Really love the servo programmer) I am very pleased with them. I think they will be great for your application (Note: the 5625 and the 5645 are the same servo...different gearset)
Best
Brian