Our intentions this year are to go Cape Horn - South Africa - Mauritius/Rodriguez - Perth, and we feel much more comfortable with this.
With respect, you're going to need a lot more luck and determination than Killarney Sailor is.
I have done a west to east trip across the Indian Ocean and I'd sooner sail to Somalia for Christmas than do that trip again.
Please be sure to check the seasonal changes very carefully because if you sail in the wrong season you will literally be beating into 25 knots of headwind for 3600 miles in the lumpiest, most uncomfortable sea on the planet.
I say this in all honesty - If I was in Cape Town and my destination HAD to be Fremantle/Perth I would either do a 1-stop trip south (35 degrees or more, on the fringes of the Southern Ocean) or I would sell my boat and fly to Perth. There is no way in hell that I would contemplate the trip you are.
If you're going to do the SA - Mauritius - Perth trip I REALLY wish you the best of luck.
For the record, I just ran a VPP study on the Mauritius to Fremantle route. In January/February you will beat for 60% of the trip and tight reach for the other 40%. In August you will beat about 50% and then reaching for about 50%. Season here is critical because of the trades that switch at certain times of the year. You have to avoid the South East monsoon.
Just my 5 cents worth - use it - don't use it.