The difference between my diagnostic and current PT score is 20 points (157 - 177.) I've been at it about 20-30 hours a week for nearly 11 months. You can surpass your goal with effort.
I'd say if you're scoring 177+ on your PT's then go for it! One of my friends scored a 172 and then studied a bit more and got a 179. He's in at Yale now.
My target score was 180. I never thought I should ever shoot for anything less. I never reached it on any prep test but I hit 177 after about 10 months.
I am also willing to mentor one person for free. Highest prep test: 177. Two-month average when finished studying: 172. Real life scores: 164/165. School starting in fall 2020: William & Mary.