Running another OS on company laptop

Question

Here comes a description of my scenario, requirements and possibilities. Scroll down a bit for the actual questions.

I want to run an another OS on my company owned laptop, no one else use it but policy disallow that I remove the old and install the new OS on the internal hard drive. However, running the new OS on external medium (USB, DVD or ext. hard drive) and virtualization is fine according to the policy.

The current OS installed on the internal hard drive is Windows 7 Enterprise 64-bit connected to the AD domain. I am administrator on the local computer so I am allowed to change some settings and install software. The simple rules is that you should not damage the computer or remove it from the AD domain.

The hardware is a Lenovo T530 laptop, CPU: Intel i5 quad core (IVT, Intel Virtualization Technology is supported), 8GB RAM, BitLocker is not enabled.

The new OS I am interested in installing is Windows 8.1 or Windows 10 (TP or RTM when it comes).

I have figured out that I basically have two choices.
1. Virtualization with VirtualBox or VMware Player.
2. Running it from an USB flash drive or similar.

1. I had virtual machines before running on different PCs but I see a two big problems with running it on the laptop. The first one is that I need to be able to use the sleep mode by simply closing the lid. Secondly, afraid of low performance and high battery usage.

2. The issues I see with is that I can't have an external hard drive which leave me with only USB flash drive as an opinion. The problem with an USB flash drive is performance of boot and loading applications. If I boot from USB I can still have files stored on the internal hard drive.

My questions:
1. Is it possible to use virtualization with the requirements that I need to have the sleep mode working and that the battery should not discharge immediately?

2. If I am going to boot from a USB flash drive. How large do I need? What would you recommend is the minimum write/read speed on the drive? Is the USB flash drive method possible to use?

My experience of virtualization is that it won't work that well on a laptop (sleep mode and battery usage). However, my experience with OS on USB flash drive is slow disk I/O which results in slow loading of applications and in general a little bit slower OS.

Besides of answers on My questions, I appreciate your own opinions or suggestions on other methods that I can use. If you need any further information, please ask in the comments.

EDIT:
By USB flash drive I mean a small one that almost disappears in the USB port. Like this one (not the specific drive or brand):

Answer 1

By my experience:

1. You can run multiple VirtualBox guests (I don't know about VMWare) and have then working side-by-side with host sleep mode. I have a Dell Inspiron running Windows 8.1 as host with 1 Windows 7 guest and 2 Linux guests (Ubuntu and Debian). When I close the lid of my laptop all the guests still on without adding extra power consumption (AFAIK they enter in a freeze state like a snapshot and after I raise the lid they continue from where they stopped, the same way if you pause the guest machine).

2. Although Linux can be installed in USB Flash/External drives I don't know if it is possible with Windows 7 or newer. New computers came with UEFI and Secure Boot and in some Linux distros you must disable secure boot and UEFI to get them working, others distros need just secure boot disabled (openSUSE 13.2 and Ubuntu 15.04 works with UEFI and secure boot pretty well). All of them uses a boot manager called GRUB2. If you're willing to use an OS bootable from a USB port you probably should disable UEFI and run in older BIOS Legacy mode. About performance, check if your USB port is at least 3.0 version and use a 3.0 USB flash or external disk to achieve maximum performance. Nevertheless you cannot compare it with internal SATA speeds you can have decent I/O speeds. IMHO: try with a USB 3.0 External SSD drive.