Very slow export FCPX 10.4 2013 MBPR

Hello

I am experiencing some very slow render / export times on a 2013 rmbp. it takes just over an hour to export a 4min video on a partially rendered timeline where the most intensive effect is color finale.

I am using omptizimed media from a ssd in raid 0 & I can see that in the activity monitor that the cpu is only getting about 15-20% use. I am currently experiencing a issue with High Sierra constantly wanting me to update my cuda driver but am unsure why this would effect FCPX.

Any advice or pointers anyone can offer will be very much appreciated.

Thanks

Chris