Dan, I know how to treat Nicds and Nimhs, I used to race 1/10th scale before 8th scale became popular, even a relatively new and fully tested Sanyo Nicd can put you in the dirt, which was my case. You do realise a 6v Nicd/Nimh pack will be above 6v for a period do you not, if the manufacturers do not put enough tolerance for .5v than I will not be buying their gear, and if you are really that worried about it, there are H.V. servos these days. The only servos i would not use are the 4.8v Futaba servos which are mainly used for heli rudder applications.

Got to move with the times my brother, Nicds are ok but not for the reasons you are mentioning and there are better and more reliable power systems out there these days.

p.s. Any battery can put you in the dirt though, lets not be naive about it.