Honestly, I wouldn't know what I was talking about if I tried running Linux over Windows, hopefully someone more knowledgeable can give you the answer you want.
I'm what you might call a 'Yay! It does Facebook and Piracy' level Linux user.
Though if I may, I suggest downloading the Bodhi ISO and either burning it to CD / DVD or by making a bootable USB stick. Both methods will let you test your Linux distro of choice without actually installing it first - though I recommend using a USB stick as the trial will run quicker. Installing it via the trial is also very easy, and has a pretty fool-proof install wizard.
Note: trialling Linux won't give you an indication of true performance speed - a proper install on your primary HDD will always work better / faster.
If you go for a USB drive, go here http://unetbootin.sourceforge.net/ and download UNetootin. This will let you configure your USB stick with your previously acquired .ISO to make what's called a 'Live CD' (unsure why it isn't called a Live Stick, though the same name is given to bootable discs).
Once this is configured, restart PC and hit F2 (from memory) to bring up BIOS and change the boot sequence so your USB drive boots first. Save and exit. You'll get the option to trial or install.
If you install, it will give you the option to format your entire HDD, or partition it into a 'dual boot' style setup. I recommend a dual boot, as it lets you keep your old OS. I've never lost any Windows files doing this but it is recommended you backup any files just in case.
I have 3 OSs on my system, Win7 for Photoshop, Linux Mint for playing around / trying to break, and Ubuntu for everything else. You switch between them by restarting your machine and selecting from a menu which pops up after the manufacturers splash.
Note I haven't used Bodhi for a while, but their emphasis has always been on fast and elegant. I put it on an ailing Toshiba laptop that struggled to run XP with 512MB RAM as a hand-me-down for my IT-illiterate baby bro. He loves it.
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Reading back, I see my post isn't particularly concise. If you want to dual boot just Google 'installing linux from a bootable usb' and you'll get a better tutorial than I could ever give.
Surprised others haven't chimed in already with their distro recommendations.
Edit: UNetbootin is just my tool of choice, there are others that do the same job.