I think some of the Gold times need a little adjustment if you want to make them competitive or whatever. For instance, most of these I got Gold pretty quickly:
Casual Level 1- Gold 2.900 / Best 1.9 / Attempts 1
Casual Level 6 - Gold 18.000 / Best 9.8 / Attempts 7
Casual Level 11 - Gold 14.000 / Best 10.3 / Attempts 2
Casual Level 18 - Gold 6.500 / Best 4.7 / Attempts 2
Casual Level 20 - Gold 23.8 / Best 14.9 / Attempts 10
Casual Level 21 - Gold 8.3 / Best 5.8 / Attempts 3
Hard Level 3 - Gold 11.000 / Best 9.5 / Attempts 14
Hard Level 6 - Gold 10.000 / Best 7.52 / Attempts 9
Hard Level 8 - Gold 23.000 / Best 21.76 / Attempts 3
Hard Level 9 - Gold 9.000 / Best 6.8 / Attempts 18
Those are the ones where it was pretty easy to beat Gold by a decent % without many attempts. Some of the other feel well tuned where it took 20+ attempts and I only got Gold by like fractions of seconds.