If you can afford it, go for masters.
Let's compare yourself to someone of your age and education but without a masters degree.
In two years, he is in great advantage (you have 0 experience, he has 2yrs). Two years later, he is still in the advantage (masters + 2yrs against 4 years). At this moment he is, unlike you, a candidate for getting a promotion etc.
But in a moment when you get ~4 yrs of experience, i.e. where you have to compare his 6yrs against your 4yrs of experience, his advantage is not that big. Four years later, 8yrs vs. 10yrs of experience does not make any difference. But your degree will remain an advantage.
Assuming that you'll work in IT for more than 2 years, I would say that your master will be an advantage for longer period that his 2yrs of more experience will be the advantage for him.
And as something possible in CS/IT, you can get some real-life experience during your masters course, which means that in practice you will have 2yrs spent on masters with some experience, and he will get only the experience.
Also, on a plus side for you, the larger company becomes, it takes more into account formal training. So if one day you want to work in some large system, it's better to have higher qualifications. In this moment you may not want that, but do you know where would you like to work in, say, 15-20 years?