To those who may be interested, SailorSat provided me the following list of modelines for each of the video modes in her software:
'15KHz Progressive
AddResolutionToTable 15, "240,240,60", "modeline '240x240@58,795' 4,83 240 252 276 310 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "256,240,60", "modeline '256x240@60,436' 5,3 256 272 296 336 240 244 247 261 -hsync -vsync"
AddResolutionToTable 15, "256,256,60", "modeline '256x256@59,496' 5,36 256 268 292 330 256 257 260 273 -hsync -vsync"
AddResolutionToTable 15, "256,264,60", "modeline '256x264@58,317' 5,35 256 268 292 330 264 265 268 278 -hsync -vsync"
AddResolutionToTable 15, "288,240,60", "modeline '288x240@59,885' 5,84 288 296 328 368 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "296,240,60", "modeline '296x240@59,941' 5,95 296 304 336 376 240 243 246 264 -hsync -vsync"
AddResolutionToTable 15, "304,240,60", "modeline '304x240@59,305' 6,2 304 320 352 396 240 243 246 264 -hsync -vsync"
AddResolutionToTable 15, "321,200,60", "modeline '320x200@59,535' 6,2 320 336 368 410 200 216 219 254 -hsync -vsync"
AddResolutionToTable 15, "321,240,60", "modeline '321x240@59,014' 6,45 321 336 368 414 240 242 245 264 -hsync -vsync"
AddResolutionToTable 15, "321,256,60", "modeline '320x256@59,917' 6,68 320 340 372 416 256 257 260 268 -hsync -vsync"
AddResolutionToTable 15, "336,240,60", "modeline '336x240@59,749' 6,83 336 352 384 433 240 243 246 264 -hsync -vsync"
AddResolutionToTable 15, "352,256,60", "modeline '352x256@59,697' 7,28 352 368 400 450 256 257 260 271 -hsync -vsync"
AddResolutionToTable 15, "352,264,60", "modeline '352x264@57,257' 7,35 352 365 405 452 264 265 268 284 -hsync -vsync"
AddResolutionToTable 15, "352,288,60", "modeline '352x288@51,116' 7,4 352 368 408 464 288 289 292 312 -hsync -vsync"
AddResolutionToTable 15, "368,240,60", "modeline '368x240@59,196' 7,47 368 384 424 478 240 243 246 264 -hsync -vsync"
AddResolutionToTable 15, "384,288,60", "modeline '384x288@51,219' 7,85 384 400 440 496 288 289 292 309 -hsync -vsync"
AddResolutionToTable 15, "392,240,60", "modeline '392x240@59,898' 8 392 408 448 504 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "401,256,60", "modeline '400x256@52,419' 8,08 400 416 456 519 256 268 271 297 -hsync -vsync"
AddResolutionToTable 15, "448,240,60", "modeline '448x240@60,01' 9,16 448 464 512 576 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "512,240,60", "modeline '512x240@59,973' 10,68 512 544 600 672 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "512,288,60", "modeline '512x288@50,939' 10,68 512 544 600 672 288 289 292 312 -hsync -vsync"
AddResolutionToTable 15, "632,264,60", "modeline '632x264@56,751' 13 632 664 728 824 264 265 268 278 -hsync -vsync"
AddResolutionToTable 15, "640,240,60", "modeline '640x240@59,96' 13,22 640 672 736 832 240 243 246 265 -hsync -vsync"
AddResolutionToTable 15, "640,288,60", "modeline '640x288@50,955' 13,1 640 672 736 832 288 289 292 309 -hsync -vsync"
'15KHz Interlace
AddResolutionToTable 15, "512,448,60", "modeline '512x448@59,863' 10,6 512 542 598 672 448 469 472 527 interlace -hsync -vsync"
AddResolutionToTable 15, "512,512,60", "modeline '512x512@58,232' 10,6 512 538 594 668 512 513 516 545 interlace -hsync -vsync"
AddResolutionToTable 15, "640,480,60", "modeline '640x480@59,536' 13,09 640 672 736 836 480 481 483 526 interlace -hsync -vsync"
AddResolutionToTable 15, "720,480,60", "modeline '720x480@59,934' 14,6 720 752 824 928 480 486 489 525 interlace -hsync -vsync"
AddResolutionToTable 15, "800,600,60", "modeline '800x600@50,546' 16,48 800 840 920 1040 600 602 605 627 interlace -hsync -vsync"
AddResolutionToTable 15, "1024,768,60", "modeline '1024x600@50,201' 20,9 1024 1072 1176 1328 600 607 610 627 interlace -hsync -vsync"
ReadCustomResolutionTable 15, "custom15khz.txt"
'25KHz Progressive
AddResolutionToTable 25, "448,384,60", "modeline '448x384@60,009' 12,95 448 456 504 520 384 387 390 415 -hsync -vsync"
AddResolutionToTable 25, "512,384,60", "modeline '512x384@59,959' 14,75 512 520 568 600 384 388 391 410 -hsync -vsync"
ReadCustomResolutionTable 25, "custom25khz.txt"
'31KHz Progressive
AddResolutionToTable 31, "512,448,60", "modeline '512x448@59,863' 21,21 512 542 598 672 448 469 472 527 -hsync -vsync"
AddResolutionToTable 31, "512,512,60", "modeline '512x512@58,232' 21,21 512 538 594 668 512 513 516 545 -hsync -vsync"
AddResolutionToTable 31, "640,480,60", "modeline '640x480@59,536' 26,18 640 672 736 836 480 481 483 526 -hsync -vsync"
AddResolutionToTable 31, "720,480,60", "modeline '720x480@59,934' 29,25 720 752 824 928 480 486 489 525 -hsync -vsync"
AddResolutionToTable 31, "800,600,60", "modeline '800x600@50,546' 32,96 800 840 920 1040 600 602 605 627 -hsync -vsync"
AddResolutionToTable 31, "1024,768,60", "modeline '1024x600@50,201' 41,8 1024 1072 1176 1328 600 607 610 627 -hsync -vsync"
ReadCustomResolutionTable 31, "custom31khz.txt"