If you can afford the 180 and have space for it, why settle for a 150?
I built a stand that can hold a 75 gallon tank, but wanted a tank so badly that I got a 55 instead of saving for a 75. I regret that now.
Bigger tanks are generally easier to care for anyway.
And with 30 more gallons, you can have more livestock.
Just my .02 cents.