Unless hes planning on building a Warbird, a 30-378 will smoke the 300 RUM on FPS after all that seems to be what you guys that insist on shooting these canons are all about.
Lets elaborate on the subject of my .284 out performing the canons. First I will run it with relatively close bullets 190 VLD VS 180 VLD that 30-378 has me beat by 250 fps by 1400 theres 14 inches between our points of impact. The 300 rum has me beat by 140 fps but at 1000 yards I have 2 inches less drop. not to mention the amount of powder or lack of Im using. Please note how awesome them fast bullets do at longer distances they fall flat on there face.
30-378 190 VLD @ 3300 fps
30-378 165 TSX @ 3475 fps
300 RUM 190 VLD @ 3190 fps
300 RUM 165 TSX @ 3350 fps
7mm LRM 180 VLD @ 3050 fps
800 yards / 10 mph cross wind
30-378 WBY - 102 inches of drop and 29 inches of wind
165 gr- 108 inches of drop and 42 inches of wind
300 RUM - 110 inches of drop and 31 inches of wind
165 gr- 119 inches of drop and 46 inches of wind
7mm LRM- 111 inches of drop and 25 inches of wind
1000 yards/ 10 mph cross wind
30-378 WBY- 187 inches of drop and 48 inches of wind
165 gr- 208 inches of drop and 72 inches of wind
300 RUM - 202 inches of drop and 50 inches of wind
165 gr- 229 inches of drop and 77 inches of wind
7mm LRM- 200 inches of drop and 41 inches of wind
1200 yards / 10 mph cross wind
30-378 WBY- 308 inches of drop and 73 inches of wind
165 gr- 360 inches of drop and 113 inches of wind
300 RUM - 333 inches of wind and 77 inches of wind
165 gr- 398 inches of drop and 121 inches of wind
7mm LRM- 324 inches of wind and 64 inches of wind
1400 yards/ 10mph cross wind
30-378 WBY- 475 inches of drop and 105 inches of wind
165 gr- 588 inches of drop and 166 inches of wind
300 RUM - 514 inches of drop and 111 inches of wind
165 gr- 653 inches of drop and 179 inches of wind
7mm LRM- 489 inches of drop and 89 inches of wind
Meanwhile Im over here- Like hows the wind and your face feeling!
Conclusion- My .284 Just smoked your big canon with that last low in the wind

and dont even think about killing an elk past 1100 yards with the 165 GR that was hauling ass at the muzzle because you are now right at 800 ft-lbs of energy