Choose the i5 10400 if you have at least 2666 MB RAM, otherwise go with the i5 8400 and 3200 MB RAM.
Choose the i5 10400 if you have at least 2666 MB RAM, otherwise go with the i5 8400 and 3200 MB RAM.
I own both CPU+MOBO options, but the 10400 only with 2666 MHz RAM (H410M card), while the 8400 comes with a Z390 supporting 3200 MHz or higher. Which set is better for gaming? The 10400 offers hyperthreading and slightly more single-core performance, but less RAM speed due to the card. Because of the motherboard...
Buy a 10400 and a better motherboard separately. That way you get the best of both worlds. Unless you are getting a significant discount on the combos, then I would just buy the 10400 combo and be fine with it. You can still buy 3200Mhz RAM and just run it at 2666, that way in the future you can upgrade the mobo.
10400 suggests that the threads would be more beneficial than increasing RAM speed.
You're using an i5-4570 with 8 GB of DDR3 RAM at 1600 MHz. It's likely you could still see performance gains, though the benefits may be limited by the older memory technology and processor architecture.