The most oft-debated question in Diabetic history I thiknk, lol.
In Canada (and me personally) we are taught to aim for a range of 7-10.0 2 hours after a meal. So, your 180 is perfect, as far as I'm concerned.
I wouldn't think you're "spilling" sugar then either, but i could be wrong.
Now, you will get different advice from different countries, and some on here are far more hardcore and think you should stay at 5.0 alll the time, but on my regime, a 10.0 (with proper basal and bolus ratios) will get me down to 4.5-7 before my next meal, so I'm happy.