I had a 184 tdi on loan for a month last year and now have a leased 150 EcoTsi.
To be honest, the 150 just doesn't have the grunt. It's really quite a noticable difference. The 150 might have a decent 0-60 on paper, but it doesn't feel anywhere near as quick as the 184, especially overtaking. In the 184, you drop down a gear or two, floor it, and it takes off! Not the same in the 150.
Don't get me wrong, I love my car. And the leasing deal on the 150 was so good that I just couldn't justify paying a hefty amount more for the 184.