Is it me or my shafts?

So I bought a range membership a couple months ago and have been practicing 3-4 times a week.  Lately, my accuracy has begun to suffer.  I've been spraying the ball all over the place with woods and irons.  Generally, I'm hitting hooks and shots that go way too high.  Very rarely will the ball fade or slice.  My wedge game has never been better though.

My irons were fitted for me (minus the shaft) for me, so I don't think lie angles or shaft lengths are culprits.  I bought the clubs online, so I didn't do a shaft fitting.  All of my clubs (except wedges) have regular flex shafts.  I read a bunch of articles and correlated carry distance with shaft flex, all of which said "err on the side of softer shafts."  So I pulled the trigger on a set of MX-1000s with Nippon 950s in regular flex.

I believe that my swing speed has increased.  I used to play a 6 iron from 150; now I play a 7 or 8 (with the same clubs).  Went to the shop not long ago and ended up playing around with a 7 wood in the simulator and it said my swing speed was around 90 mph.  It was a regular flex, and I was hitting hooks.  I then grabbed a Mizuno MP-57 3 iron with a PX 5.5 shaft just to see if I could hit it, and I struck it pure (ooh that buttery feeling), carried it 195 straight as an arrow.

My question is, would a stiffer shaft help me?  I don't know my driver or 5 iron swing speed, but like I said, my 7 wood speed was 90 mph.

Based on how you described your accuracy faults i dont think a stiffer shaft will drastically make you hit it straighter. It could probably help but not fix. And dont think because you hit a few good PX shots that you should get them. PX are not the most user friendly shaft in the world. Of course if you get fitted and they recomend them then by all means go for it. The articles you read were right about going with the softer flex. Your swing has to be more precise the stiffer your shaft is.