Its difficult, and dont I only know it, that when you have a long term goal on your mind such as pro flight training its easy to be in a rush.
In your particular case, and for what my opinion is worth, I think you should get your degree first and keep your ppl valid during that time.
You will still only be 23 when you've got it and will be say 24 or 25 when you have a frozen atpl too. Thats a lot better than being 21 with ONLY a frozen atpl, and the employers I'm sure would look at this way too!