Just remember there is 10 main gear teeth per every 1 tooth to the pinion.
14/150 ratio is 10.714
12/121 ratio is 10.083
There is .631 more turn on the main gear from the 150 to 121. Not much head speed more, but a little.
Just FYI, helical cut gears are made to be quieter. The straight cut slaps together when the main and pinion teeth meet up whereas the helical gently rub together from top to bottom, or bottom to top. And you get a little more tooth surface.
All cars on the road today have helical cut gears in the transmission because they are quieter. If you bust open a racing transmission, they are straight cut. It makes for faster shifting and more strength on the straight cut, but also more of a gear noise.