Laptops and emulators and shaders

[schadenfreude]

I'm planning to buy a new laptop, and for portability's sake I am aiming for something with around a 13" screen size. For gaming, I plan to use it to play emulators of old computers/OSes: Apple II, Commodore 64, DOS, etc. I prefer not to emulate real consoles because they're easier to acquire and set up, but you might be able to help me with my questions if you've been using other emulators on a laptop.

Here are the questions:

• In general, how is emulation on OS X these days? I currently use a 15" MacBook and might just get a 13" model. I currently run Windows 7 in a Boot Camp partition, but I don't want to have to reboot my system every time I want to fire up an emulator. What about running my emulators in a Windows VM?
• What are my options for shaders? Are they emulator-specific? And do I need a nice graphics card for this? I doubt the machine I settle on will have a dedicated GPU. I can live with "decent" shading/filtering, since the games I'll be playing are old and will mostly look like ass no matter what I do
• What's it like running old system emulators on these high-resolution screens, like the Dell XPS 13's 3200x1800 or the 13" Retina MacBook Pro's 2560x1600? I imagine shading will look better with higher resolutions, but is it significantly better?

That's all I can think of for now. I'd be grateful to read your opinions if you have experience in any of these areas. Thanks!