Catalytic Converters - what size??

The exhaust on my 3.3ltr V6 Pathy has had it and I’m in the process of arranging to have it replaced with a 2 ¼ system. The old system has 2 inch pipes and 2 x 2 inch catalytic converters.

I have been told to upgrade the catalytic converters at the same time as the pipes/muffler. One place has suggested 2 x 2 ¼ inch normal cats, another has suggested 2 x 2/14 inch high flow cats and yet another has suggested 1 x 2/4 inch high flow cat (2 pipes in / 1 out).

Now I am confused as to which way to go. Obviously it would be nice to pick up a few extra hp. I would have thought that 2 x standard 2 ¼ inch cats would be an improvement over the current set-up???

Does any one have any experience or suggestions on which way I should go???