I have played with both the MX100 R300 steel (which I own) and the JPX800 R300 steel (for two 18 hole rounds). They are very similiar but I use the 7-9 for various open fairway pitch and run shots and I found the JPX 7-9 a little too "hot" for my taste. I did try the JPX800 Pro, and to me that is a very different club; more like an MP. The MX100's seem to feel 'softer' but the JPX800's seem to go a bit farther. A friend and fellow golfer just purchased a set of JPX800HD with graphite R300 shafts and they feel very nice and not so hot in the shorter irons.
As for the forged issue, I have previously owned both MP30 and MP60 irons. With age, I needed more forgiveness and found with the MX100 irons I have more control. I do use MPT 11 wedges and feel the forging does make a difference with scoring clubs.
I started playing at 17; I am 68 with a 17 handicap.