Yup, it's fine, the voltage rating is only the maximum it can take. Lower voltages make a smaller and lighter cap, that's all.
If you can find 6.3v ones, get them. I use them with my solar robots, and are nice and compact. Just make sure it's used for the receiver
. The 1000uF I use is 3/8" diameter, 1/2" long. Otherwise, a 10V will do just fine. The 4700's will be much bigger, but not too bad, at 5/8" diameter, 1-1/4" long or so.