Despite dire warnings from some people there aren't any flys on the 458. The original problems dealt much more with poor bullets than the slower velocity. With new powders, and even factory loads, 2200fps is available.

Add in the better bullets available now and the 458 is as good as any of the British Calibers. Some people feel that if they don't have the most than they don't have enough.

I have no idea about turning your rifle into a CRF. I think that with enough creativity and money anything is possible. I know a guy who turns Remington 700s into CRF actions. I would check on cost as opposed to buying another action or complete 458.