Still, unless you know how you react to bupe, you're best off starting with less. Given how much you've been using 2mg should be enough to keep you from feeling acute withdrawals. The best part is, you can always take more. Bupe is an extremely strong drug, so be safe. Frankly I'd be amazed if you really were to need more than 2mg to stay well. More than that there's a good chance you'll get high, or sick...
Frankly, 8mg is more than you need in any absolute sense, but you can be the judge of that.
The only bit of the above I find myself in absolute agreement with is that, between dosages of bupe you should wait one to two hours. Takes a bit to kick in, although not quite as long as methadone ime.