The experts now have all lined up!
As the poll already indicated, the consensus is that you can only take more room - to do a tactical rounding - if you also have right of way as an inside boat. I was send an scan of an article in Yachting World by Mike B (thank you for that and also thank you, Jose).
In it John Doerr, who previuosly stated that a boat could sail her proper course from the moment she entered the zone, now explains she cannot if she's only entitled to mark room and thereby corrects his earlier interpretation. An inside keep clear boat breaks a row rule, if she takes more room then needed to sail to the mark and will not be exonerated for breaking that rule by 18.5.
Read the whole article here: The Knowledge march 2009
I'm glad we got that sorted out, only 99 more to go....