Ditto on casingboolits, I started casting last year and there is no better source of information out there. Many of them have been doing it 20-30+ years.
1:8 will leave you in the 200gr+ arena. From what I've read, 240 is the easiest to develope subsonic for.
ANOTHER great resource is:
http://www.lasc.us/CastBulletNotes.htm