His post-season goal-scoring domination in his era was probably along the lines of Bobby Hull (if we're breaking tradition and assuming McGee's era was weaker than more modern eras, otherwise...). From 1903 to 1906, his goal-scoring finishes were 3, 1, 1, and 1. He led in goals per game every Challenge he played in. And yes, he beat up on Dawson with 14 goals in one game that time, but he still led his own teammates by quite a margin.
1903:
Player|Team|GP|G|G/GP
Jack Marshall|Montreal|4|7|1.75
Billy Gilmour|Ottawa|4|5|1.25
Frank McGee|Ottawa|2|4|2.00
Billy McGimsie|Rat Portage|2|3|1.50
Tommy Phillips|Montreal|4|3|0.75
1904:
Player|Team|GP|G|G/GP
Frank McGee|Ottawa|8|21|2.63
Alf Smith|Ottawa|7|13|1.86
Tommy Phillips|Toronto|2|1|0.50|Note: also had 2 assists, a rarity
Jack Marshall|Montreal|1|1|1.00
Harvey Pulford|7|1|0.14
1905:
Player|Team|GP|G|G/GP
Frank McGee|Ottawa|4|18|4.50
Alf Smith|Ottawa|5|11|2.20
Tommy Phillips|Rat Portage|3|8|2.67
Silas Griffis|Rat Portage|3|3|1.00
Tom Hooper|Rat Portage|3|2|0.67
1906:
Player|Team|GP|G|G/GP
Frank McGee|Ottawa|4|16|4.00
Harold Smith|Senators|5|15|3.00
Alf Smith|Ottawa|4|7|1.75
Marty Walsh|Queen's|2|4|2.00
Frank Glass|Montreal|2|3|1.50
George Richardson|Queen's|2|3|1.50
1907:
Player|Team|GP|G|G/GP
Ernie Russell|Montreal|5|12|2.40
Lester Patrick|Montreal|6|10|1.67
Tommy Phillips|Kenora|4|9|2.25
Frank Glass|Montreal|6|8|1.33
Ernie Johnson|Montreal|6|5|0.83
... I probably should have done this before voting started.