rib,
Just some things to consider...........
If your beam on your 268 is 8'6", the width at your swim platform will be less. Therefore if you had a 8' 9" inflatable (for example) on davits while backing into a well, your inflatable would touch the dock or piling before the rub rail of your boat. Not a good thing if the dock or piling has sharp edges, nails or whatever sticking out.
When we had a 26' Doral Citation with 8' 6" beam we had a cheap Seylor inflatable that we used with 2 hp Honda 4 stroke outboard. The inflatable we bungie corded on the swim platform.
When we had a 30' Doral Prestancia we had actual weaver davits and had a quicksilver 8' 9" inflatable on davits. The Prestancia was a 10' beam.
On our 328 Vista Four Winns we purchased a new 310 Mercury with Burk Davits and the inflatable is 10' 2" and the 328 beam is 11 9". The inflatable is about the same width as the 328 when sterning in.
Anyways with a 8' 6" beam I'd be ok with a 8' 9" inflatable or similar, but just be mindful when sterning in.
I think you would find that a inflatable less than 8' 9" in length would be crowded with three adults aboard.
If you do a lot of exploring in an inflatable (like we do) a bigger inflatable is better. Just be careful as mentioned above with backing in with your inflatable on.
Have fun with your decision.
P.S. I see you are from Listowel, Ontario, I assume most of your boating will be out of Lake Huron around the Bayfield area?
Mike.