In my games i usually get to a point where i do not need more research world (especially on larger maps) and end up with a lot of wealth worlds and i usually play on slowest research speed. the main problem is that technologies do not scale with map size (afaik). However just increasing tech cost based on map size would severely slow down the early game.
So my simple suggestion would be a scaling factor (or at least an option for it) that works like this:
for every tech researched every further tech cost +x%
for example on a medium size x could 0.5, so when you have 100 techs your 101 tech would cost 50% more. on a larger map x could be 1, so when you have 100 techs your 101 tech would cost double the base research points of that tech. this would particularly make a big difference between players with a lot of research points on larger maps and later in the game whereas the early game would be nearly unaffected no matter the map size.
