NO, do not convert your HDV to ANYTHING else before editing. (sorry David) Especially another highly compressed format. Set up a D1 8 bit timeline and edit your HDV Firewire captured footage in there. DON’T let FCP change the sequence settings to match your first clip. If your footage is 1080i FCP will put a shift fields filter on each clip. If you shot 30p, all the better.
You will need some kind of card to do the downconvert to your monitor and Beta deck on the fly, Blackmagic and Kona are excellent for this. You will have to render but it will be normal render times, not the lengthy conform times in an HDV edit. I use this workflow daily and it looks as good or better than any Betacam footage I’ve ever used.
Have a wonderful day.