Take it from someone who has been in this hobby for far too long,
You will not stop at one tank so why not make your next Tank the bb version ?
Trust me lifes too short changing from I/R to BB when you could be spending that time painting, weathering and fitting out your M4 to make it YOUR Sherman.
Your Tank will spend most of its time on a shelf and no one will notice the BB/IR conversion but you can look forward to lots of positive comments about the paint job.