I've been using callaway X16's over the winter season, and im starting to get used to them, but i've got the chance to get a set of Ping ISI's cheap. Are they better clubs than the callaway's or should i just stick with the steelhead X16@s?
Hard to say. I'm not a great fan of these particular Ping irons. I tried Ping irons every now and again throughout the 1990s and i.m.o. the new stuff is more to my taste.
Although I don't use Callaway irons (not keen on the chunky look and offset) they are jolly good clubs.
X-16s are rated as very forgiving (did they do a tour version?)
I had a set of X14's and absolutely loved them. I don't think the X16 were that much different and so my answer would be to stick with what you have as you have invested the winter getting to know them.
The alternative is to see if you can borrow the Pings for several rounds and see how they react. Personally I don't like Ping but that is just a personal preference. They may suit you but my choice would be the Cally's