Frank, I can't remember right off hand, but if the 9650 isn't digital it will probably burn up. I really can't tell you who told me, but someone very knowlegable about this subject told me they have had no problems running a good quality digital servo wit the spektrum and with no voltage regulator.
If the 9650 is analog you could simply put a resistor inline from the battery to reduce voltage. You can do that in this situation b/c the only thing really drawing any current is the servo. I believe the one that comes with the FET KO servos is a 470 ohm, but I'm not absolutely sure about that.
FYI, I mentioned to Eric @FMA Direct the other day that he should offer a 6V version of their small 5V regulator and he told me it wouldn't be hard. In fact, I bet if a couple of you guys called www.fmadirect.com
or emailed them, he would jump on that pretty quick. It's a very easy modification and requires hardly any retooling.
Another option many don't know about is the Novak regulator harness. It works great and includes a switch just like the little GTX switch. You can glue them side-by-side and they look great. If you are good at soldering you can shorten the wires to clean up the look on your car too. You can find it here- http://www.shopatron.com/index/126.96.36.1990.0.0.0