Again +1 on the EGW Bases. I run a flat EGW picatinny base on my 300WM also.
Nice solid mount for the Burris Signature Z Rings. They might not be as 'taticool' as the TPS rings, but they will allow you to correct for any imperfections in your mounting and alignment arrangement and obtain a perfect alignment.
Also they do not have to be lapped in order to assure adequate ring to scope contact to prevent slippage. The Posi-align inserts will not mark or mar your expensive scope also.
When it comes to equipment and weapon system set up, the little things that didn't mean much at 100-500yds will suddenly jump up and slap you in the face when you start going beyond 600yds.
Biotin works good to help grow back the hair you'll pull out while trying figure out the little things that add up to big things in long range shooting!
Have a great time, it's worth the trouble... and hair!
Animo et Fide "Courage and Faith"