Need some advice on expansion/spinoff

[amagab]

I currently run a sorta busy forum/gallery/blogs running vB 3.8.x

The forum is dedicated to a certain area of discussion but there has lately been more popular to discuss other areas of interest. I have therefore purchased a vB4 Suite license and am planning to spin off and move the appropriate subforums to that site.

I am faced with member issues. What would you suggest I do?

1) Create the new community, move the appropriate subforums and copy the member table. Old members are able to login on both sites, new members would have to register on each site.

2) Create the new community, upgrade to vB4 on both sites, pay a developer to create a hack so that both forums run off of the same database, members only need to register once.

What is you advice? I know #1 is more easier and cheaper for me but #2 will probably make members happier and create more traffic.

Thanks!