Lower gear to go down hills?

Lower to me, and I think most is a lower ratio which is an easier gear. IE, the big cogs with lots of teeth on the rear cassette.

Going from a 48/32 to a 52/36 or 53/39 might be a big change for you. I've been riding a 52/36 for the last 5 years and am thinking of going to a 53/39. I used to run a 7 speed 14-28 rear with a 53/39 and found it easy enough for all but one very long hill in my area that suddenly steepened to over 10 percent grade shortly before the top.

So it really depends on your terrain for your ride and your fitness level. Take a look at the lowest ratio gear combination you routinely use to keep you from walking your bike up the hills you ride. If that will still be an available ratio when you put one of those cranksets on your bike then you'll probably be good. Also take a look and make sure the ratios you normally ride cruising won't be on the 1st, 2nd or 3rd cogs of your cassette (the low gear ratios) for those cranksets. I usually look to keep my cruising cogs on the 5th or 6th thru 8th or 9th cog of an eleven speed rear.