If you want heavy yielding plants then you must avoid very early flowering strains, usually early flowering strains with a 8-9 week flowering time are far to be the best yielding plants.
It's true that indica and indica dominant hybrids are very fast flowering and perform very well indoors, but it's better to choose sativa/indica hybrids or high yielding sativas to achieve great yields outdoors in a climate like yours.
Koodense gave you very good recommendations (thanks!).
If you don't want to harvest later than October, then i recommend you a sativa/indica hybrid like Orient Express, Zamal Hash and Malawi x PCK. They are all heavy yielding strains of moderate flowering time (around 10 weeks).
If you want to grow sativa then Malawi, Panama and Zamaldelica are high yielding sativas suitable for your climate and latitude.