Adult finger size, or regular 'wedges' are a good size. So I would continue to cut the size you are cutting.
I wouldn't go small, as Amanda has said if they can't pick it up they can't choke on it but being unable to pick up isn't the aim is it
I once saw a small button that had fallen off DS's cardigan. It was right next to him and I saw it just before he did so I got to it first. it frightened the hell out of me. It was right then that I realised I'd rather he had a plastic plate in his mouth than a plastic button iyswim. Bit of a drastic exaggeration for an example but bigger is better IMO.
One thing I did which you might find easier to begin with, is not offer 'hard' foods. So I didn't give cucumber, raw apple, raw carrot, toast or bread sticks. Anything that could snap off and not mush in his mouth I avoided for the first few weeks. Toast was a worry for me but went in and down very well when I tried it a couple of weeks in. But raw apple he still has a problem with even now at 17 months! He has just recently been able to eat raw carrot.
Like Katy said, you're almost at the 6 month mark, waiting another couple of weeks isn't really going to stop him swallowing things whole. We started at 5.5 months (really was no option) and your DS is showing readiness by the simple fact he is putting food to his mouth and chewing it.
Steamed veg sticks or backed wedges are a good place to start as they are firm enough to be picked up but the inside is soft and mushes in the mouth without denying LO the pleasure of discovering the real texture (in the way that purees all have the same sloppy consistency).
