Question 1st PC Build Upgrade: Best Bang for the Buck?

Aug 1, 2020
Hey all, looking to upgrade my first ever PC build from 6 years ago.

Approximate Purchase Date: the closer the better

Budget Range: ~400 After Rebates; After Shipping (flexible on this; looking to hear suggestions)

System Usage from Most to Least Important: gaming, surfing the internet, 3D modeling

Are you buying a monitor: No

Parts to Upgrade: Looking for suggestions

Do you need to buy OS: No
Please note that if you're using an OEM license of Windows, you will need a new one when buying a new motherboard.

Preferred Website(s) for Parts:
No preference. I am in the USA, so looking for best price here.

Location: Corvallis, OR, USA

Parts Preferences: none

Overclocking: Maybe?

SLI or Crossfire: Maybe? I think this motherboard supports it

Your Monitor Resolution: I have dual ASUS monitors 1920x1080

Additional Comments: Play steam games mostly, familiar with windows, 3D modeling, and programming

And Most Importantly, Why Are You Upgrading: General computer slowness. Gaming performance is pretty poor.

PC Build:

CPU: Intel Core i5-4670K 3.4GHz Quad-Core Processor
CPU Cooler: Noctua NH-U14S 55.0 CFM CPU Cooler
Motherboard: Asus Z97-A ATX LGA1150 Motherboard
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1866 Memory
Storage: Samsung 850 EVO 500GB 2.5-Inch SATA III Internal SSD (MZ-75E500B/AM)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive
Video Card: XFX Radeon R9 290 4GB Black Edition Double Dissipation Video Card
Case: Cooler Master HAF 912 ATX Mid Tower Case
Power Supply: XFX 650W 80+ Bronze Certified ATX Power Supply
Optical Drive: Asus DRW-24F1ST DVD/CD Writer
Operating System: Microsoft Windows 8.1 (OEM) (64-bit)
Monitor: Asus VG248QE 144Hz 24.0" Monitor

Thank you!
With a $400 budget you have to choose between a CPU/motherboard/RAM upgrade or a GPU upgrade. While for gaming an i5-4670k still works, 4c/4t CPUs are running on borrowed time. It isn't uncommon for me to have performance issues on my work desktops i5-6400 due to only 4c/4t. GPU wise the R9 290 is basically equal to an RX 480 4GB so it is still OK for 1080p gaming. Since you are doing 3D modeling, it might make sense to do the CPU upgrade.
PCPartPicker Part List

CPU: AMD Ryzen 5 3600 3.6 GHz 6-Core Processor ($159.99 @ Amazon)
Motherboard: MSI B450 TOMAHAWK MAX ATX AM4 Motherboard ($124.99 @ Best Buy)
Memory: G.Skill Ripjaws V 16 GB (2 x 8 GB) DDR4-3600 CL18 Memory ($62.99 @ Amazon)
Power Supply: Fractal Design Ion+ 660 W 80+ Platinum Certified Fully Modular ATX Power Supply ($119.99 @ Newegg)
Total: $467.96
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2020-08-01 16:36 EDT-0400

This includes a PSU upgrade as well. Your PSU is getting up there in age and since you would be removing the motherboard, adding a good high efficiency PSU isn't a bad idea.