One problem you have is that local internet is what the companies are basing their maximum rates on. It used to be that there was only one trunk line from here to the US, for example, to Florida I believe (maybe more specifically Miami). If you are trying to communicate with places outside of South America, for example, you may be caught up in the maximum bandwidth that can be carried by that main line to the US (some times are going to be heavier than others). I don't know if that line has been upgraded or added to, but it used to be one of the limiting factors a few years ago.
Also, you have to deal with ping, which is how long it is taking your communication to reach the destination and return. Distance plays a part in that, as well as infrastructure. The more possible paths you have to get to your destination, for example, the lower the ping will likely be even over distance. For example, when I used to test my connection to Brasil, I used to get a horrible ping even while getting a decent download rate for the most part.
I have Fibertel's 6 MB still, which I upgraded to about 3 or so years ago. I find that it does reasonably well for me, although admittedly I'd like to have something faster, but a lot of the work I do are to servers in Austin, TX, to which I always have a fairly high ping, though decent bandwidth, close to my 6 MB limit, at least at night and in the wee hours when I typically work.
I've been thinking about upgrading to Evolution though...