there could be scenarios*, where disk IO constitutes the largest portion of time consumed during operation - IO heavy operations. they are often found in a normal desktop usage. there, the difference in storage IO speed impacts performance much more significantly, than in the example of running some stupid command. for example compiling linux - the most beloved occupance for many enthusiasts. 
ok, more seriously, say, - paging (incorrectly called swapping). exactly browsers are the first candidates to cause paging. paging out megabytes of browsers' bloat to a 12-25MB/s vs. 200-400MB/s (writes) storage makes practical difference, the experiences will compare like "crappy" vs. "nicey", "meh, ewww" vs. "not bad, impressed". also, more space of SSD means less wear out, which is imo even more important, than higher speeds. but yeah, nothing comes for free. insane speeds of NVMe come with the increased power consumption and heating. but the OP asked about speed difference.
that said, still, personally, I'd go with an eMMC on PBP, due to the mentioned heat characteristics of SSDs, because for me, it would be very incomfortable to worry all the time what's inside of the firmly filled laptop, aren't its guts melting down? but it's about people's characters and needs. I am minimalist and won't use too demanding software. for others, using some bloat is requirement. then putting more capable (both in speed and volume) storage would be benefitial.
* and there are scenarios where slow storage IO speed is a show stopper. my android tablet refuses to play video from an SD card lying me, the files are "broken", whereas it's IO that is too slow. my PC plays them, just sometimes missing frames.
ok, more seriously, say, - paging (incorrectly called swapping). exactly browsers are the first candidates to cause paging. paging out megabytes of browsers' bloat to a 12-25MB/s vs. 200-400MB/s (writes) storage makes practical difference, the experiences will compare like "crappy" vs. "nicey", "meh, ewww" vs. "not bad, impressed". also, more space of SSD means less wear out, which is imo even more important, than higher speeds. but yeah, nothing comes for free. insane speeds of NVMe come with the increased power consumption and heating. but the OP asked about speed difference.that said, still, personally, I'd go with an eMMC
on PBP, due to the mentioned heat characteristics of SSDs, because for me, it would be very incomfortable to worry all the time what's inside of the firmly filled laptop, aren't its guts melting down? but it's about people's characters and needs. I am minimalist and won't use too demanding software. for others, using some bloat is requirement. then putting more capable (both in speed and volume) storage would be benefitial.* and there are scenarios where slow storage IO speed is a show stopper. my android tablet refuses to play video from an SD card lying me, the files are "broken", whereas it's IO that is too slow. my PC plays them, just sometimes missing frames.
ANT - my hobby OS for x86 and ARM.
