And there were numerous instances where pilots took out MGs to save weight with the logic if they couldn't hit with 4 they wouldn't hit with 6. The "Superbolt" took 4 of the 8 MGs out in an effort to increase performance. Many of the MTO Spit drivers took out the 4 303s and relied only on their 2 cannons in an effort to increase performance.
Keep in mind that many of the best 51 drivers scored the majority of their kills in 51Bs. Don Gentile, Duane Beeson being two examples who never flew D models in combat. Richard Turner of the 354th FG has written in a couple different places how he felt the Malcom hood, P51B was the best of the Mustangs with better visibility then the D, and better performance.
I guess it is much about personal preference.