Early 2009 iMac and Sierra

I'm guessing performance may not be as great as it is with Sierra vs El Capitan on an early 2009 imac regardless of the fact that I have upgraded memory to 8GB and have replaced the hard drive with an SSD.

However, just from a curiosity perspective the app store keeps prompting me to download MacOS Sierra. Is it possible that it can be downloaded and installed regardless of the fact that I have an unsupported imac?

I do understand that there are ways to install Sierra on my imac (eg, http://lowendmac.com/2016/macos-sierra/) but I'd rather do it via the supported App Store channel.

Has anyone else with and early 2009 imac tried to download and install via the App Store?

If yes how was the performance?

Hi,

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac, then choose More Info. These Mac models are compatible with macOS Sierra:

• MacBook (Late 2009 or newer)
• MacBook Pro (Mid 2010 or newer)
• MacBook Air (Late 2010 or newer)
• Mac mini (Mid 2010 or newer)
• iMac (Late 2009 or newer)
• Mac Pro (Mid 2010 or newer)

macOS - How to Upgrade - Apple

The most important thing to remember when upgrading from one OS X to another is to backup all your important data beforehand.

The installer simply will not let you install.

The installer will inform you that it cannot be installed.