Ping S series and I series

Father, forgive me for I have sinned. I am 31 years old and toying with the possibility of buying some Ping irons.

Right, formalities out of the way!

Is there a big difference between the Ping S series irons and the I series?

I am considering them as never met anyone who has a bad word to say about Ping clubs! I know the G series are too bulky for me as I play with a guy who has the G15 but wondering what people think of the I or S series....

Thanks in advance