600/Regent/Normal and Marathon, depending on how bored i am.
It's just that most Civs have 2-3 cities that can spam cities for colonies. Portugal has 1 and a half, with Ponta Delgada being only used for settlers and Funchal is so poor in culture that it's a city used just for the Sugar.
The thing is that of all the colonial powers, only two have no neighbours to worry about: England, and Portugal. Portugal with the caveat that you "suck up" to Spain, which really isn't that hard. Both England and Portugal don't need to invest hammers into defence as a result: England b/c its an island, Portugal b/c two of their cities are islands and their capital is basically impenetrable to AI Spain until the mid-Renaissance. Those hammers can instead go to boats and to settlers, while France and Spain need to invest in units (mainly to defend against one another).
Then, comparing England to Portugal, Portugal starts later but with a more developed capital and a substantially better army, and likely better improved land due to the two other Iberian civs. It's perfectly possible to coast off Lisbon with bare minimums in infrastructure investments, while London starts with nothing but a Granary. Further, you have a much better army with Portugal, which only needs to defend one city - Lisbon - so you could take all the hammers you might need to invest for England and pump them all into infrastructure in Lisbon. Lastly, if you're looking at UHV's, England needs to colonize hostile land (sans Australia) to do its UHV, so it needs to make units, and also needs to pump out Frigates and sink ships for UHV2, while Portgual has one free basin of settlement (Brazil) and can concentrate any excess military on Africa for defence.
So you have a situation with the colonizers where there's a top tier of colonizing civs (England and Portgual) who can theoretically invest all their hammers into colonization, a good tier of civs poised on Western Europe with good land and lots of historical territory (Spain and France) but who need to defend (or conquer) their neighbours, and then a tier of civs who
could colonize b/c of their position and land but lose a lot to do so (HRE, Vikings, Moors).
The point I'm getting at is that while Portugal's land and cities suck prima facie, there's a lot of factors actually militating in their favour, not the least being the strength of Lisbon as a capital. It starts with infrastructure, a substantial defensive garrison, improvements, and is already an A-Tier capital in its own right with one of the best BFC's in the game. Ponta Delgrada and Funchal admittedly suck but as you note they can pump out settlers due to being coastal cities. In direct comparison, the other Western European colonizers might just seem strictly better, city by city, but the geopolitical situations of each and UHV objectives also need to be considered.