Unless your apps are 64 bit enabled, and can use lots of ram, the upgrade is probably not worth it.
OTOH if you do lots of multitasking, then 8gb might be good.
I assume you also have a 64 bit os to be able to use >4gb.
If you do plan on an upgrade, and why not, since ram is so cheap, I would just get a second 4gb stick to match the one you have.
It turns out that the current intel cpus are largely insensitive to ram speeds, so 1067 is plenty. You can only tell the difference with synthetic benchmarks, not real app performance.
If you want a real boost to your laptop performance, see if you can't replace the hard drive with a SSD.