BMW aus's site says that the 20d has 130kw and 350 nm and the 23d has 150kw and 400nm. Thats why i assumed you could chip the 20d to the 23d power levels. I have seen these gains on other diesel engines, but i'm sure these engines from BMW might be a bit different.
Fraser, Have you had a chance to take one for a test drive yet? 7.3 sec to 100 for the 23d sounds like fun