For a first-time cruise, I would tell people to go for longer if they can, simply because these ships are THAT big, and there’s a lot of stuff to see and do. 5 days (or is it 5 nights?) is just enough time to get familiar with how things work on board, but, IME, not quite enough time to really enjoy it thoroughly (I kind of speak from experience… due to leaving for our honeymoon the day after the wedding, being awake for nearly 40 hours and exhausted from all the festivities, we kind of slept through our first day and a half of our 7-day cruise! By the time we started learning the ropes, we had to start thinking about packing up and leaving! That’s largely why we took another one 18 months later, by coincidence on the same ship!)
I think it comes down to how much money you want to spend, but for the difference in number of nights, you aren’t paying that much more. I would guess that the “partially obstructed” view would still leave a fair amount of viewing space… looking at pictures on Google Images, it looks like the lifeboats would block your view of the sky, but not of the water or any ports of call you go to.