A basic idea of where you need to be at the end of each level if you want to break a million, given start score "x". (This chart does not figure death or kill screen points, since the Rule of Donkey Kong Screwings makes it safe to assume that most deaths will be worth about 200 points. Better to play as if you won't get any points for your deaths.)
If Start =
L=04 100,000 105,000 110,000 115,000
Running Total Goal =
L=05 152,941 157,647 162,353 167,059
L=06 205,882 210,294 214,706 219,118
L=07 258,824 262,941 267,059 271,176
L=08 311,765 315,588 319,412 323,235
L=09 364,706 368,235 371,765 375,294
L=10 417,647 420,882 424,118 427,353
L=11 470,588 473,529 476,471 479,412
L=12 523,529 526,176 528,824 531,471
L=13 576,471 578,824 581,176 583,529
L=14 629,412 631,471 633,529 635,588
L=15 682,353 684,118 685,882 687,647
L=16 735,294 736,765 738,235 739,706
L=17 788,235 789,412 790,588 791,765
L=18 841,176 842,059 842,941 843,824
L=19 894,118 894,706 895,294 895,882
L=20 947,059 947,353 947,647 947,941
L=21 1,000K 1,000K 1,000K 1,000K
Avg 52,941 52,647 52,353 52,059
The difference between a million pace with a 100K start and a million pace with a 115K start is 900 points per level. In other words, getting to a million after starting weak will require the equivalent of one additional barrel smash or double-jump for every barrel screen.