Coding in .NET 3.5 with 2013

At the moment all in house development is accomplished using Visual Studio 2010 SP1 and .NET 3.5. We are presently evaluating migrating some applications to a new SharePoint portal and are debating which version to install - 2010 or 2013. Our doubts revolve around the seemingly new requirements for 2013 (http://technet.microsoft.com/en-us/library/cc262485.aspx), especially .NET 4.5.

If we install SharePoint 2013, will we still be able to develop code for SP using VS2010 SP1 and .NET 3.5, or will we be forced to upgrade to VS2012 and use .NET 4.5 (which is really 4.0)?

Thanks,

Reuvy