Your shortcut should point to:"C:\Program Files (x86)\Maxis\SimCity 4 Deluxe\Apps\SimCity 4.exe" -w -r1600x900x32 -CustomResolution:enabled -intro:off -CPUPriority:low -UserDir:"C:\Users\USERNAME\Dropbox\SimWINNER\Fileshare"
Add -CPUPriority:low -UserDir:"C:\Users\USERNAME\Dropbox\SimWINNER\Fileshare" to your "Launch Options", as well as any custom resolution you want.