I run two operating systems on two separate disk partitions on the same physical machine (a modern MacBook Pro). In order to isolate them from each other, I've taken the following steps:

1. Configured /etc/fstab with ro,noauto (read-only, no auto-mount)

2. Fully encrypted each partition with a separate encryption key (committed to memory)

Let's assume that a virus infects my first partition unbeknownst to me. I log out of the first partition (which encrypts the volume), and then turn off the machine to clear the RAM. I then un-encrypt and boot into the second partition. Can I be reasonably confident that the virus has not / cannot infect both partitions, or am I playing with fire here? I realize that MBPs don't ship with a TPM, so a boot-loader infection going unnoticed is still a theoretical possibility. However, this risk seems about equal to the risk of the VMWare/VirtualBox Hypervisor being exploited when running a guest OS, especially since the MBP line uses UEFI instead of BIOS.

This leads to my question: is the dual-partitioning approach outlined above more or less secure than using a Virtual Machine for isolation of services? Would that change if my computer had a TPM installed?

Background:

Note that I am of course taking all the usual additional precautions, such as checking for OS software updates daily, not logging in as an Admin user unless absolutely necessary, running real-time antivirus programs on both partitions, running a host-based firewall, monitoring outgoing network connections, etc. My question is really a public check to see if I'm overlooking anything here and try to figure out if my dual-boot scheme actually is more secure than the Virtual Machine route. Most importantly, I'm just looking to learn more about security issues.

EDIT #1:

As pointed out in the comments, the scenario is a bit on the paranoid side for my particular use-case. But think about people who may be in corporate or government settings and are considering using a Virtual Machine to run services or applications that are considered "high risk". Are they better off using a VM or a dual-boot scenario as I outlined? An answer that effectively weighs any pros/cons to that trade-off is what I'm really looking for in an answer to this post.

EDIT #2:

This question was partially fueled by debate about whether a Virtual Machine actually protects a host OS at all. Personally, I think it does, but consider this quote from Theo de Raadt on the OpenBSD mailing list:

x86 virtualization is about basically placing another nearly full kernel, full of new bugs, on top of a nasty x86 architecture which barely has correct page protection. Then running your operating system on the other side of this brand new pile of shit. You are absolutely deluded, if not stupid, if you think that a worldwide collection of software engineers who can't write operating systems or applications without security holes, can then turn around and suddenly write virtualization layers without security holes.

-http://kerneltrap.org/OpenBSD/Virtualization_Security

By quoting Theo's argument, I'm not endorsing it. I'm simply pointing out that there are multiple perspectives here, so I'm trying to find out more about the issue.