Let's compare (Games like SMK will only take the time that is the fastest time from either so NTSC/60hz and PAL/50hz don't get their own different categories and all times are non SC/ non PRB)
(SNES-Wii)
Track Og. Game Time MK7 Time
N64 Luigi Raceway 1'38"13 1'42"876
GBA Bowser Castle 1 41"20 1'11"161
Wii Mushroom Gorge 1'41"625 1'33"637
DS Luigi's Mansion 1'30"954 1'43"281
N64 Koopa Troopa Beach 1'19"51 1'30"314
SNES Mario Circuit 2 1'01"63 1'08"313
Wii Coconut Mall 1'56"158 1'56"339
DS Waluigi Pinball 1'56"962 2'11"103
N64 Kalimari Desert 1'43"32 1'34"221
DS DK Pass 1'43"902 1'57"207
GCN Daisy Cruiser 1'36"205 1'26"397
Wii Maple Treeway 2'16"100 2'16"832
Wii Koopa Cape 2'18"936 2'06"785
GCN Dino Dino Jungle 1'41"429 1'49"773
DS Airship Fortress 1'43"696 1'54"140
SNES Rainbow Road 1'23"71 1'12"948
I will try to update this list as much as I can so that people can easily compare times between two games and see if tracks have been shortened or extended

.