Personally, I didn't get overwhelmed, but I'm the sort of person who seems to remember things well, or have things click for me easily (at least in my chosen subjects because I'm absolutely useless at maths and chemistry. Would NOT have remembered stuff so easily with those A Levels.)
You have to remember it's essentially one extra lot of class time, workload and revision load/time for you to do. I'd say only take 4 if you really really really can't choose only 3 subjects (which was my problem. I was doing 4 and didn't want to drop one when second year came around because I like them all) and if you're sure you don't mind having less time than your peers.
I guess to compare, the college I went to had periods of 1hr 30mins. There were 4 periods in a day plus a 45 min lunch. So that's 20 periods per week. Each A Level Subject I took was 3 lessons per week (except Spanish which was 4 lessons, because it's a language). That's 13 lessons a week. So 7 free periods. So 35% of my college hours was free time. My friends only did 3 A Levels (and no languages) which meant they had 11 free periods - which is about half of their college hours. (not including lunch period)
So there's less time but more work. I had 4 sets of prework and homework to do each week, or each day etc. (Some subjects had regular schedules, others didn't). The college recommended about 4.5 hours a week of work/revision. That's over 16 hours a week. And I had about 10 and a half hours of free periods a week (not including lunch or weekends). If you think you can do that, then why not? Also, you can always drop it if it gets to be too much anyways.