2 months vs 4 months for internship?

Hey monkeys,
I'm a first year at a top Canadian school (not Ivey or Queen's). I got an summer internship offer from a tech company. This company asks me if I want to start in May or in July. My summer starts in May but I was thinking about taking some extra credits in the summer to take some loads off my fourth year for CFA, GMAT, interviews, etc..

Question:
All else being equal, is a 4 months internship worth the opportunity cost of taking summer credits?
How is a 2 months internship perceived by employers?
NOTE: the tech comp has a very big project coming up but that's all the info I have.
Any opinion is appreciated. Thanks.