It's slightly faster and slightly more money. For many things, you likely wouldn't know which was which.
Ivy Bridge has a few features not found on Sandy Bridge that aren't directly related to performance. These might matter more than a slighter faster clock speed.
Ivy does a little more work per clock cycle than Sandy, so the 3% difference in clock speeds understates the difference a bit.
If you were being paid to do a particular task repeatedly, it might do the job in 3 minutes and the 2120 might take 3.2 minutes. If you had to do the job 1000 times, the slower machine would take 53.3 hours and the faster would take 50 hours. They say time is money, but it might not matter to you.
Since you aren't buying for at least 6 months, I wouldn't get bogged down in these details yet. Re-examine the situation a month before you will buy. There may be new processors at that time and prices will certainly vary due to sales and searching for different vendors.