Yes, you can. But; remember that some chips do not like extra voltage or perform no better with them - while others can tolerate higher voltage and do allow room for more performance. That all being said it will require you to do benchmarking between settings to determine whether you A) notice a difference, B) see viable returns in the benchmarks, and C) are able to maintain stability.
So - when overclocking RAM you get two things or both depending on which ways you go - snappier performance or more bandwidth.
In real world terms you'll ultimately notice snappier performance (gained by lowering latency, timings) before you notice increases in bandwidth, unless you run very specific programs that can gain a boost by having that extra bandwidth (scientific datasets, extremely large Excel spreadsheets, etc). Games will generally not show any performance increases with either, unless you make large jumps from say DDR2-533 to DDR3-1600, probably in loading times and not much else.
That's a little more than you had questioned -
Lastly - voltage can and does ruin memory and newer memory seems to like less increase in voltage than previous incarnations of chips. So be careful how far you go. 1.65 to 1.7? Probably no problem. But 1.65 to 1.75? Probably not a good idea without adequate cooling and reliable stress testing.