Yep, that desktop should do well in medium to high settings for Sims 3 and all it's expansions/stuff packs.
However, I should note the disclaimer of - please keep in mind there will still be some lag, stuttering and slow downs with Create a Sim, Create a Style and build mode. Also the more content you add like store content, custom content, and mods the more the game will lag. This is due to the way the game handles additional content. Not much can be done to speed that up, unfortunately. But it is far less noticeable on a desktop.
Thanks for asking!!