Performance tests were just published today, please look at:
https://www.macrumors.com/2019/03/28/2019-imacs-geekbench-benchmarks/
Should provide you with all the information you need, the 2019's are much quicker than your 2013 however without knowing how you use your computer it's impossible to state whether you would benefit or not. In addition, if you get a 21.5" model only purchase with16GB or greater RAM and a SSD, otherwise it won't matter much.
Finally, the article states if you are considering upgrading from a 2017 iMac then performance increase is not that great. What that means to me is to search for an Apple Refurbished iMac which has zero downside. They have an identical warranty to a new Mac, are eligible for AppleCare, are identical to new, can be returned to Apple for ANY reason within 14 days of purchase and can save hundreds of $. If you are not familiar with them visit Apple.com navigate to the bottom of the page and look for the refurbished link. If you don't see what you want then check often as inventory changes VERY fast.