Hi Casado.
Im going to be in Samui grinding sitngos for a month starting next week. I've been there about 5 times previously.
The internet in Samui is variable. I have found a lot of hotels and bars have poor wi-fi connections, but there are a couple of internet cafes around that have good, reliable fast connections. I suspect that they have access through a different company.
At this point my plan is to test out the connection in my hotel
http://holidayparksamui.com/, and if that is no good I will attempt to buy a monthly membership to one of the reliable cafes (eg offer them 1500 baht or so for allowing me unlimited usage of their connection.
An unreliable connection isn't great for cash games either, as it can result in the client not posting your blinds in time. But you are right in that a loss of connection during a multitabling sitngo session can be disastrous.
I would forget about Koh Pan Gan, the infrastructure there isn't nearly as good as Samui.
PM me for my email address, I'd be happy to share any info or experiences.