i7-4770 or i7-4790 would be compatible w optiplex 9020.

e.g., https://www.amazon.com/Dell-OptiPlex-9020-Desktop-Computer/dp/B00IO5VJKS
https://www.amazon.com/Dell-Optiplex-9020-Quad-Core-Professional/dp/B00T6H8GIG

4790K works but needs the optional 365W power supply. 365W unit is only for the TOWER model.  If you have 9020 Micro model this is not a possible upgrade.

This is a proprietary 8 pin power supply.

https://www.moddiy.com/products/Dell-OptiPlex-9020-PSU-Main-Power-24-Pin-to-8-Pin-Adapter-Cable-30cm.html

Hi @JTownGLI,

Going from quad core to quad core often doesn't yield much improvement.  We don't know the exact CPU you have yet.  But for example, if you went from an I5-4590 to an I7-4790, it only yields 25% performance improvement according to game-debate.  That's only 1.25x performance increase, barely noticeable.  It's noticeable when it's almost double.  Then it'll show in green instead of red on the game-debate site.  Screengrabs will be below.

Often switching to an SSD and/or increasing RAM makes a more noticeable difference.

Images show once approved by a moderator.  It takes longer on the weekends.

Respectfully, I still stand behind game-debate, in which the 25% performance increase almost seems to be an average of what HWBench gave.  This is not meant to disagree with HWBench.

So I did a comparison with the I7-4790k.  Game-debate gave it a 33% performance increase in green font.  Though not almost double, the percents looked a lot better in hwbench .  Just a reminder PSU's would need upgrading with the k version.

When I switched CPU's in a PC, game-debate gave it a 64% performance increase.  I didn't notice much difference.  Switching to an SSD and increasing RAM made that PC fly.  Boot time (though not the biggest thing) was down to 17 sec. with Win10.

So @JTownGLI,.there's the presentations with final decision making up to you.  (Though this is based on not knowing your exact original CPU yet.)

Reasons to consider Intel Core i7-4770:

• 8% higher single threaded performance (not much)
• Much higher multi threaded performance (around 35% higher). This allows for higher performance in professional applications like encoding or heavy multitasking.
• Around 21% higher average synthetic performance.

http://hwbench.com/cpus/intel-core-i7-4770-vs-intel-core-i5-4570

i7-4790k is a great cpu starting at 4.0 Ghz. Caveat for -k cpu: Dell bios does not support OC. if you buy used you need to be careful the cpu was not OC'd too much by previous owner(s).  this piece of history is hard to get. if you hear seller say it was never OC'd, it is almost certainly tongue in cheek.

you can use of-the-shelf 24 pin to 8 pin adapter if you want to upgrade the stock psu to regular 24 pin ATX psu. https://www.amazon.com/Eyeboot-8-Pin-Supply-Adapter-Motherboards/dp/B01A210HKO

I can't edit my post above.  It looks like 'edit' is now on a timer.

Are we sure a PSU upgrade is necessary if going to an I7-4790k, to go from 84w to 88w?

No need to upgrade psu for -k cpu in optiplex because you can not OC. When you OC a cpu there is significant more power draw.

Hi @zEddie27,

Both the I7-4770 and I7-4770k are 84w.  So yes, the 290w PSU can power it.  Just remember there's no provision Dell Optiplex BIOS for OC.  If you use a GPU, it would have to be 75w or less.

would the i7 4770k work without a 365 watt power supply? I am building my own dell 9020 MT using the PC5F7 motherboard. with the traditional 290 W dell 9020 power supply

Hi @zEddie27,

I'm using Dell Optiplex 9020 with i7 4790 for 2 years now, no problem whatsoever (I don't use discrete GPU, use stock power supply). Recently upgraded to NVME SSD using x16 expansion slot, NVME SSD run at full speed, but careful with the heat, installed 3x 4cm fan at the back to dissipate hot air. Hope it helps.