Change default font from Helvetica Neue to Helvetica

Helvetica Neue for small characters is just plain annoying to read on my 2013 non-retina iMac (while on my macbook retina I recon it looks good).
But just setting everything to Helvetica (with developer tools) improved the user experience a lot, as one can see on the attached files.

My suggestion:
1) enable users to set other fonts as default;
2) identify if the screen is retina or not, and automatically set fonts accordingly.