Sounds like you have felt the distance between the two clubs and rightly noticed a couple of differences.
The sgi clubs will typically differ in distance, especially if you have a little less weight on the bottom of the player's cavity backs and catch them a little thin. They will go a mile further!
Also, when you hit your new clubs toward the heel or the toe of the club face you should lose a lot more distance than you did on your off center hits on the sgi clubs.
On a different note altogether...sounds like you should really drop the 25 bucks and at least get fit for the irons you are going to play with. The length of the club and the lie of the irons should be adjusted for your current posture and play. I don't know anyone who would hope to improve and enjoy the process with clubs that are not at least the right length! It doesn't cost much and the sweet shots would be much more common!
Most big box golf stores (Golf Galaxy to name one) will take about 30 minutes and measure your swing and make some recommendations. If you are really a 10 handicap, you are ready to get clubs that fit you.
What new clubs did you get?