My actual Linux X5650 is xeon_linux01 and it shows 44KhS but only pulls 28K H2pS on average. Sure, that's a decent margin, but I'm running a very stripped down version of Xubuntu off a USB, so I would expect a somewhat higher actual rate. Windows is pretty bloated in that regard and it can only be a drag on performance. So on average, my Linux box is about 15% faster. That's certainly within the realm of reason.
Running Linux off a USB stick might actually be slowing you down. I did for a while and noticed odd delays, which turned out to be I/O delays reading and writing from/to the USB stick. In the end it fell over (although part of that may have been the age of the USB stick and heat causing contact issues on the connectors).
A spare hard drive or an SSD would almost certainly be better, or working out how some distros load themselves into a ramdisk before booting, so the USB stick is not required while it is running.