More RAM in SQL should give you an increased performance as long as it is allocated to the SQL server in question, SQL Server should "seize" a lot of that RAM on the startup of the service.
Unless you are doing a lot of computations on the recordsets returned then having excess CPU will not increase SQL Server's performance. I would recommend the second option with 6GB of RAM. If you use parameterised queries this should allow a lot more of the queries that are executed more often to have their result sets stored in RAM rather than having to be "extracted" from disk.
Of course, RAM or CPU is not the only bottleneck in SQL server, look at your disk layout and RAID levels, please see http://serverfault.com/questions/118767/standard-database-backup-procedures/119123#119123 for another post on here about how I have configured my servers, this is by no means expert advice but I have found it to be performant in my environment.
Make sure to do regular backups and remember it's not a valid backup until you've tested your restore!