I would use a solid carbide drill bit for the 1/4" holes, and drill them first.
Then follow with the 3/8" downcut with a helical toolpath.
The 1/4" hole will provide some clearance and greatly extend the life of the tool. Since those are small holes, the feedrate will be fairly low, so try to keep the rpm as low as possible to maximize tool life.
I'd recommend a downcut bit with a harder grade of carbide, like a Vortex XP.
https://www.vortextool.com/index.cfm...F089BBBA600C0D