OK test animation works a treat, havent tried hands yet but everythng else translates exactly, in that whatever the low-rez model is doing the exported BVH file makes the high rez V4.2 do exactly the same.

Problem solved, nice smooth scrub line without any lag or fram skipping  whilst working on the low rez model greatly aids in tuning the animations, then once its all done export to BVH, delete the low rez model, load the high rez model and import the BVH.

Thanks again Nightfall!!