In my boats I don't like to cover the whole floor. It makes the drop floor too big and awkward to transport. I usually end up with a floor that covers the rowers foot area and extends to the pasengers foot space. A total length of about 3 bays. The bays used for big coolers or big dry boxes don't need a floor since the cooler or dry box is hung from straps and fills the whole bay.
For bulk gear like dry bags, camp chairs, tents etc. I prefer using an 'everything bag' from Tuff River Stuff. This is a huge mesh bag with a draw string top that hangs in my rear bay and acts like a suspened floor. I don't need to worry about strapping each item to the boat, I just toss them in the bag and cinch down the top.
The Revolutionary Everything Bag
Each boat seems a little different in design and rigging. It depends a lot on personal choices and the gear you hope to haul. It also tends to get modified over time as I change my mind or rig for a different length trips.
Since I'm a cheap bastard and own some wood working tools my floors are home made from marine plywood and painted with outdoor patio paint (holds up better than spar varnish). I can easily modify the design as I see fit and it doesn't break the bank. I have even added last minute tie points at the put-in using a cordless drill.
Since the suspended floor doesn't touch the raft bottom I don't see how different floors could effect the boats performance. Full length floors might effect how the boat can flex going over an big rock, I would probaly cut a full length floor into 2-3 sections so it could flex with the boat. As for standing, in my experiance 1/2" plywood was too wimpy, 3/4" or 5/8" would be a better choice depending on the distance between supporting straps. I like to cut a lot of holes in the floor to let water drain quickly, maybe 1 1/2" dia. holes at 8" on center each way, in staggered rows. I use a 1/4" radius router bit on all the edges and corners. Make sure the holes are big enough to pass the cam buckles. That many holes will weaken the plywood, so the 3/4" seems about right.