I have set up 8 of our laptop users to connect to the mail server using RPC over port 80 both inside and outside of the office. In the Proxy settings in Exchange, just check off both options for slow and fast networks.
In my testing, there has been no difference in speed between the standard tcp/ip connection and the rpc/https connection. It has been nice to eliminate the firewall though. (if you hold down the CTRL key and right click on the Outlook icon in the tray, you can see the connection type)
All of the users only have one profile to use. You just need to make sure that you set up an A record in DNS pointing to the mail server for users on the Lan.
The only problem I have run in to is configuring an RPC user from outside of the network which the exchange server is on. On all of the machines I configured, the initial connection had to be made on the Lan that the Exchange server was on, and then the machine would work fine from wherever it connected, but I have been unable to make that initial connection outside of the local lan.
Hope that helps.
Mark