I'll put my two cents here, and would like to say before anything that I might be wrong here, I'm far from being an expert more like a regular amateur
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If you can feel a noticeable difference in the air being sucked into the engine I would say you either have a problem with compression (piston rings, valves) or your cat converter is clogged which creates backpressure and will lower the ability of the engine to create vacuum. Both a compression test or a vacuum test should help on determining what's your exact problem. I would just do both... I'm not sure, but think I remember reading from other members in the forum that you can rent both compression and vacuum gauge testers at most autoparts stores (loan program).
You could try disconnecting and removing the pre-cat O2 sensor to see if the air flow changes.
I'm pretty sure someone else will chime in; in any case I hope this information helps.
Oscar.