I am measuring the actual usage. And while ram may be cheap, memory controllers aren't infinite, I am already using 4 sticks of RAM and only had 4 slots. Anyway, the measurement is on Windows with Bitcoin-Qt/Core default settings.
Presumably if your system was made in the last decade it support modules larger than 2GB?
What is the virt usage corresponding to your 800 mb actual usage reading?
As for git master, what are the potential side effects of mining on it?
That it may crash or end up forked and leave you effectively not mining. This is also true for any other version, but non-released versions are (by definition) less widely tested. The amount of risk depends on whats going on recently in git master. At the moment, there isn't anything exceptionally new which is obviously highly risky. Similarly if you keep coins on that system exposing immature software to the internet you might have an increased risk of a security compromise. That said, hopefully you have no coins on the system considering you're using it for web-browsing. Marginal risk from new code in bitcoin core is going to be much less than running any browser.
If your hashrate is only fairly modest (I'd hope— since you're not running your node on a separate dedicated system), you could just consider a bit of risk taken here as a public service and increase your monitoring vigilance to match. If you were talking about a large amount of hashrate, I'd recommend against not— not just due to the risk to yourself, but if you start producing multiple invalid blocks it may cause (minor) problems for SPV nodes or alt implementations. Risk that you take on your own is one thing, subjecting other people to it is another matter.
My hashrate is highly modest, you wont need to worry about it
. As for your other statement, I do actually keep coins on the system I am using, and whats more the wallet is unencrypted. However, I am vigilant. I've disabled Java, Flash and watch what I download, I don't download any email attachments, nor look at emails from my spam folder other than for giggles. I also recently acquired the skill of reverse engineering, although still in its infancy, however I have a pretty good idea of the APIs windows malware use, the point is unless I trust the source, I'd inspect any software in a VM before I let it run on my system.
It would be foolish to think I am 100% protected, but I've also considered implementing some custom protection specifically to deter any attempts at compromising my wallet.