When are graphite iron shafts ok?

Hi everyone,
I was wondering if anyone had any advice as to when graphite shafts for irons are ok before you have to cross over to steel shafts. I just got my clubs over ebay. The person was nice enough to have sent over the original steel shafts along with the installed graphite shafts. Any recommendations? Should I change back to the original steel shafts? My swing speed is around the 85-90mph range. The current shafts that I have in the irons are Fenwick Graphite Shafts with regular flex (are these any good?). The steel shafts are Ben Hogan Shafts. Thanks

Yun

P.S. - when quoting swing speed.... which speed do we use? I thought the speed changes with different clubs due to the changing shaft length. I figure my driver should be faster than my pitching wedge.

There is an excellent article about shafts in the June issue of Golf Tips. The article goes into weight, torque, bend point and swing speed and provides details about specific shafts from different manufacturers. What I get from the article is graphite is lighter and absorbs shock better but steel is more consistant.

I switched to all graphite last year, at the age of 46. I prefer the light weight and have noticed the difference in reduced vibration especially on mis-hits. I noticed also, that because the club is lighter, I tend not to muscle the club as I did in the past with my steel shafted clubs, which leads me to beleive that I would have benefited from using graphite at an earlier age.

Note that I now play a lot more than I used to, so my game has improved in the past 2 years from playing in the 90s to in the 80s. So I am considering going back to steel shafts in the future, although high quality ones.