Gave it a few more tries this afternoon after reading some more about this game.
45,000 - Wow and I only made it to round 4. Tried some new strategies.
1. Pipes, get them early as before, but I read online that if you shoot 2 pipes in a row of the same color, you get 4x the score. This can be huge as early in the round the pipes are worth a lot of points. Problem is, the screen is littered with items to hit and every hit of something else reduces the point value of the pipes. Not only that, but the 2 pipes you hit of the same color must be hit on consecutive shots without hitting anything else. This is hard as hell to do. Seems that if you can clear 1/3 of the items (Ducks first) than you can find some gaps to shoot the pipes and go for the bonus.
2. Ducks, you need to pick them out and keep targeting them to clear them from at least the bottom and middle rows before concentrating on pipes if you want the 4x bonus, otherwise you'll have a red pipe gone and need another, but here come the ducks to eat your bullets.
3. Bonus, wait as long as possible before shooting the letters for the bonus. The higher up the item is, is not only a higher score when you shoot it, but also adds that same value to the bonus. Ideally, you'd want the b-o-n-u-s letters to be the last ones on the board.
Not sure if I can top the last score, but maybe. I've made it to round 5 a few times before, If I can do that and employ the strategies above it's definitely doable.
Good Luck!