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is there a more logical way of doing it
There are two approaches, the one I've been using for 30 years and the one normal people use. I set my bike up by the book in 1988 and just replicate the position on each new one because nothing about it annoys me. If that's where you were with the Tarmac, then it's a viable option for you, and you'll just have to suck the aesthetics of a rising stem since you bought a new bike with so much less stack.
The alternative, and a good investment if there's something about your current position which annoys you, is to go to a good bike fitter and let them tell you what's best for you. @scherrit seems to be the forum favourite, but others are available.
gbj_tester-
It was a bike fitter than put me on the 100mm -6 degree on the tarmac.
I guess my next question is, if I were to ride a -6,-8 degree stem which would mean around 40mmish lower on the front end. How would be the negatives to this? Would it just be super uncomfortable, or is it just the way they wanted the bike to be? Lower and aggressive? There is only one size up after this one and the reach is a beyond my current on the tarmac.
Is there any negatives to riding a positive degree stem, other than it looking terrible?
inkleined
On the Tarmac I am running a 100mm -6° degree. The Cipollini has now arrived and I have a 110mm -17° degree stem to play with, unfortunately it looks awful flipped to 17°. I really don't want to run it like that. I understand that is the best way to get it to near enough the same position as the tarmac. Not really sure what to try in terms of length and degree to get a suitable riding position. Would it just be a case of trying a variety and see what feels ok, or is there a more logical way of doing it.