Wyatt's Box Help

[Tiny Tim]

I have a Remington 700 in 300 RUM that I'd like to put an extended box in. I am uncertain of whether the MBE-2 or MBE-3 is the proper one. I could also use the CFE-12. All have the same basic internal length. Is there an advantage to moving to the center feed? Was also looking at the CFE-9. This gives almost 4" internal capacity which may be beneficial for the 215 Berger Hybrid and longer bullets. If using the CFE-9, do you also have to open the rear of the ejection port to remove a loaded round? If so, does this affect your optics rail mounting? Looking to better understand my options.