Since it is only $100 more I’d recommend the quad-core i5. Even with the thermal limits of the processor it should still be faster than the 2017 base MacBook Pro. That said, the screen on your 2017 will be a bit better (wider color gamut and higher maximum brightness).
I think it's only faster for short-bursts not for sustained work.
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Lol kind of wrote the whole question in the title. But I am not a computer person. However I am curious to know if the new air with the better keyboard will be slower than what I already have.
I think I am in a good place to answer this.
I have a 2017 MBP 6-core i7.
Just purchased for partner 2020 MBA i3 (base model)
The MBA is faster in launching every app I have tried so far.
The MBP is faster at exporting photos and exporting longer videos (but not noticeably faster for short videos).
The MBA is quieter with no fan noise or uncomfortable heating of the case when doing video conference calls.
The MBP runs it's fans on jet plane mode on video conferencing after about 20-30 minutes
* video conferencing includes Zoom, Facebook, and Skype for business (virtual), and Teams
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Since it is only $100 more I’d recommend the quad-core i5. Even with the thermal limits of the processor it should still be faster than the 2017 base MacBook Pro. That said, the screen on your 2017 will be a bit better (wider color gamut and higher maximum brightness).
Depending on your requirements I would not recommend the i5. It runs hotter, is less silent, and has worse battery life of around 10% than the i3.
If those things are not a concern, then by all means the quad core might be a better choice.