Oh come on.
All you need to do to keep Windows 7 running as quickly as on the first day is to keep the autostart clean. win+R -> msconfig
It is not that difficult but so many idiots install all kinds of BS software that wants to autostart. And stupid magazine keep telling the people that emptying caches makes anything faster.
Windows 7 runs fast and it also runs faster than OSX. OSX has a great GUI but it is from a technical perspective not an objective opinion to regard it as the faster OS anymore.
If you care about performance a custom desktop build is very fast when you add gaming performance into the mix the Mac Platform is no competition.
A 2500k with a decent aircooling runs 4 GHz overclock. Can only be beaten by multisockel board which again don't cost the world. You just need a huge case to stuff it in.
iMacs run mobile GPUs. Desktop GPUs are both faster and they are really easy to replace. After 2 years to switch them for a new upper midrange GPU and you play top graphic engines at high detail again.
Speed, memory, processor, hdd, ssd - doesn't matter with Windows. It's not a hardware problem, but a programing problems - too much legacy BS in windows.
That is the kind of answer you can expect in a Mac forum. Needless to say it is utter nonsense.
The truth is building a custom PC (some shops even assemble them for a small fee) is not very difficult. Keep Windows 7 running fast and quick doesn't require any more work than on OSX. Just keep Autostart free of BS. I have seen so many fools that install every little crap they find and never use. Naturally it will be slow as crap especially on these old Notebooks. You just clean autostart. That stuff can stay stored on the hard drive as dead data but it won't affect performance.
Legacy support slows nothing down. That is just some myth.
Truth is Windows has some of the most advanced schedulers of all OS. The definitely most advanced memory management and the usability is not so bad either anymore.
But if all you need is a media PC. For some videos, little browser games, office work. Just get a Mac Mini and some display or get a Notebook. If you don't need the power just get that small box and a box for NAS data storage and you are well prepared.
If you want gaming. Nothing beats a custom build + a decent monitor 24-27". It is faster you can pay for the best quality, best performance and it is real easy to upgrade.
For many of OSX gui features there are little Tools that enable the same functionality in Windows. Just ask in a Windows forum.
Really ask yourself what is the functionality and speed you want.
Windows 7 + custom build is like buying the iMac that comes out in 2 years now in terms of speed.
If you want a mighty mouse, this touchpad or some other OSX functionality get a Mac.
I have a 15" MBP(which I like very much) and some experience with custom building PCs. Don't trust the Mac fanboys they just know one side and have little to no clue about the other.