Exchange 2010 Routing Groups

Hi,

I recently setup Exchange 2010 in a 2003-2007 mixed environment.  Mail is flowing between all servers but is taking extra hops when going from 2010 to 2003 and vice-versa.

Setup is as follows:
Exchange 2010 - Site #1
Exchange 2003 - Site #1
Exchange 2007 - Site #2
Routing Group Connector (Cost = 1) - Setup between 2003 and 2007

I want to have all mail between 2010 and 2003 route directly between each other instead of via 2007 which is in a separate site.  If I create a RGC between 2003 and 2010 what cost should I apply to this to ensure I achieve desired results?

Also, will mail between 2003 and 2007 still go out via original connector?  Ideally I want 2003 to route mail directly to 2010 and to 2007 without any extra hops.

Thanks.