I ran Rem 700s for years in hunting rifles--factory and custom--and had just about every type of issue you can read about: Failure to feed, failure to extract, broken extractor, AD, heavy galling. I have had none of those issues with CRF M-70s, and the M-70s allow at least the same level accuracy and strength.
All that said, if someone already has a 700 and wants to build a custom, it is less expensive to use their existing action. We charge $200 to true a 700, though I am still not sure that is completely necessary. The factory trigger and bottom metal can be reused.
To Compare:
We can buy an entry level BAT Machine action for $1050. It needs a trigger which adds $200 and bottom metal and mag adds another $275. So that puts the complete action at $1525. It is very strong, well machined, true, and reliable. The trigger and bottom metal we pick will be excellent.
An American Rifle Company Nucleus Gen2 CRF action is $1000. It needs a trigger which adds $200 and bottom metal/mag adds another $275. So that puts the complete action at $1475. It too is very strong, well machined, true, and reliable. The trigger and bottom metal we pick will be excellent.
A Rem 700 SPS can be had for $600-$700. Add $200 for truing. The trigger and bottom metal are serviceable. That puts us at $800-900.
A CRF M-70 can be had for $1000-$1200. Add $200 for truing. The trigger and bottom metal are good. That puts us at $1200-$1400.
There are factors other than cost and accuracy. If you are going all out on a build, with a $750 - $1000+ stock, a full $500 cerakote "pattern" job, a $2000+ scope, A $200 titanium brake, $825 for fitting barrel, brake, and bedding; $600 fluted barrel, $350 bottom metal, $200 trigger; then maybe spending another $500-$1000 for a custom action is the better call.
So there really isn't a wrong answer.........