IMO, the biggest con for raid5 is the one im finding out now: expanding it. to expand it, you basically have to buy 4 disks at a time which is expensive (upgrading my raid5 to 3tb x 4 is going to cost me about 550 euros).
go for the largest raid5 you can; if not you might regret it later, like im doing now....
You should only need to purchase one extra drive to expand your RAID array. If your controller requires you to add four extra disks then there is something very wrong with that controller and I would recommend changing to something else. I've used HighPoint, LSI and Adaptec cards and all three of those have supported capacity expansion by adding a minimum of one new drive to the array. They also have all supported adding 2-3-4+ drives at once.
The only reason your card would ask for more disks is if you were changing raid modes from say RAID0 or RAID1 to RAID5 or from RAID5 to RAID6 while simultaneously expanding your array size at the same time.