Top marks to this man! Possibly the most sensible and unbiased opinion on C Vs Bow I have ever read!

Excellent work mate

You're not the first to come to the dark side. 18 months ago I came across after 8 years windsurfing and haven't got my old gear wet since. It really is a great sport with a lot of diversity to offer with it. Your windsurfing background will help immensely as your understanding of the wind etc. is already there. Learn to control the kite and your away. As for the kite styles etc. Without telling you to suck eggs, the C kites were the "first" kites and the "depowered kites" that you refer to are the Bow Kites and derivitives thereof in SLE's and Hybrids. The C Kites have excellent safety systems pretty much standard these days with a 5th line that enables you to let go of everything and have 100% depower. They don't have as large of a wind range as the Bow style kites and are slightly more difficult to relaunch when you drop them into the water. Some traditionalists however wouldn't kite on anything else.
As for the Bow kites, they offer greater depower and yes in effect sort of make a big kite a small kite as well as the safety that accompanys this. Its basically the same as with windsurfing when you simply sheet out. The surface area is the same but you're exposing less of it to the wind. However this works in reverse as well, as that same surface area can be used to your advantage and presented to the wind for greater bottom end which = getting on the water earlier. They are much easier to relaunch when dropped and because of these factors are generally considered a better option for beginners in todays market. Having said that, I have recently bought myself an SLE kite and absolutely love it, so I have sort of gone in reverse. (i.e learnt on C's and now on SLE) Some people will also say the Bow kites are too heavy on the bar pressure (sheeting in and out) but it depends really. As I have said, I have an SLE that the bar pressure is super light and gives the same feel as a C kite when unhooked. (Same as windsurfing again, say when wave riding and unhooking for carving on the wave.)
As for comparing kites and sail sizes. In short no you can't. When kiting started they used to say whatever sail we were on, kiters were basically on double. With all the technology etc. going into improving performance with the kites now (as mentioned above) it is no longer a good comparison. Most kite manufacturers however will have a wind chart with their kites, generally applicable to a person weighing 75 kgs or thereabouts. Like windsurfing though this is a general rule, it depends on ability and the type of board being used. A rough guide only. Anyway I hope this helps a little.

Cheers,

Fozzy