I think it is a personal decision.
If it feels right to you, go for it.
I happen to like the 40 degree feather, over anything between 0 and 90.
Edit added later after thinking about your question:
I got to thinking about how I ended up at 40 degrees. and it came from the paddle guru.
Like most long time kayakers, I started out with 90 went to 70, 60, 0 - did not feel right at 0 at all, finally 45 until more or less standard then for me was and Is 45 until I called Jim Snyder of JimStyk fame and had him build me a paddle (I asked for the one designed like he uses and got a "cruising" model via UPS some months later. I had seen this same paddle down in Mexico on a waterfall running trip as two of the others on the trip had been river guides with Jim and let me test out their JimiStyk paddles one day. To this day, that is the easiest blade to paddle I have. The smaller blade is really nice and works most of the time just fine. I found tho that when I got the Burn, I needed a larger blade to get the boat to respond the way I thought it should. So in the Burn I use my hand lay up Sidewinder slalom blade made before they were purchased by the big boys and now may not be made anymore. If I buy a glass paddle I go for 45 still. On glass I like the Werner DD thick blades.
Go to
http://www.jimisnyder.com/html/the_feather_rap.html
and read Jim's thoughts on paddles.
I consider Jim's work to be the best I have found anywhere. A close second in quality plus design and less bucks to buy, is Mike out of Salida CO and Cricket Paddle Co. Both guys hand make to order. Mike told me his goal as a paddle maker was to be as good as Jim. Well, he is gettin real close.
Anyway, you can read this post and the URL and hopefully that will help explain paddle feathering..
If you just play boat, 0 feather is prolly just fine, if you do a lot of river running especially out west with afternoon wind and big holes to blast thu - the feathered blades might help.
Like I said, if it feels right to you, then it probably is.