Wow, thank you all for your responses and information. Happy New Year by the way.
I've read through each and every single post meticulously. You've all given me a lot to consider! So much so, that I think my brain is about to burst!
I have to admit, I'm also ecstatic to see fellow aussies chiming in on the discussion as well. You guys are basically saying that really the only fully synthetic oils in Australia are the 5w-XX oils am I correct? If so, does that mean the Nulon 10w-30 / 10w-40 "Full Synthetic" oils aren't actually fully synthetic even though they claim to be? I remember reading a review somewhere stating that that was the case, as I was actually considering using these oils too.
In regards to the oil leak, I believe it's coming from the corner of my valve cover, so I'm planning on getting the gasket replaced at Honda in the near future. Hopefully that would be all that is needed, but I fear that there may be additional leak locations that need to be addressed as everything is actually very oily when looking upwards from underneath the car... The suggestion from Pepsibottle1 to put some dye into the oil next oil change is unprecedented to me and seems like a great idea. I think I may just do it depending on how costly and effective it is.
When it comes to sales on oils in Australia... it seems like I've just missed the decent ones for 5w-30 fully synthetic oils, with the most recent sale (Castrol Edge) being around 2-3 weeks ago. I've been keeping a lookout but haven't spotted anything yet, and I can't say that these kind of sales are very common. Although, I'd like to thank SR5 for the heads up on the 10w-40 Magnatec sale at Autobarn. I would have probably picked one up had I not already had a few spare 1L bottles of HX7 left in the garage.
In all honestly, my original thoughts about buying a full syn. 5w-30 have only been strengthened by the comments from OVERKILL and Shannow (In addition to the link provided by B320i for HM 5w-30 oils, I didn't know it was possible to get HM oils of that viscosity here in Australia). However, I am still considering the 10w-30 / 10w-40 Nulon route if they are actually proven to be fully synthetic. I am indeed also aware that if I switch to the lighter oil my oil problems will probably be exacerbated (and my wallet problems too hehe), but I feel like it will be a good thing that I will at least be more inclined to fix the root problem instead of just covering it up as B320i stated. I would just have to cross my fingers that the oil leak can be solved without much strife.