That's not a Desktop. That's a cellphone conection and processing power that, by todays standards, reassembles a phone more than a laptop.
But even on mobible, latency is a much bigger problem than file size.
>"hitting a bug in one version but not the other" issue shouldn't be more significant than the current "hitting a bug in a third party library (jQuery) which I don't have the expertise to locate+fix" issue that we already have to consider.
All things being equal, you have twice as many chances of hitting a bug with two code bases than with one.