Pocket C+4 has a very good speed and compatibility. It also supports today's most advanced VGA devices in their native 480x640 resolution. 

Here's a list of features:

•  Full 7501 (CPU) emulation:

• all documented & undocumented opcodes,
• 100% correct decimal mode,
• instruction/cycle exact emulation.

• Video/Sound (TED) emulation:

• very fast Line-based emulation,
• all display modes,
• open and expanded borders,
• DMA cycles, some FLI modes, FLD effects
• Timer and raster interrupts,
• raster line exact hardware cursor & flash
• 2 channel sound supporting digi

• Full ROM banking, support for the built-in C+4 programs
• Full joystick and keyboard emulation
• DOS-based 1551 drive emulation
• Support for .prg, .p00 and cartridges
• Support for true VGA resolution
• Redefinable d-pad
• Sticky keyboard option
• Expanded full screen modes for optimal display usage.
• Support for native and software landscape modes
• Full menus and keyboard controls in landscape mode.
• Full save/load emulator state support
• External keyboard support

 
For more information head on over to the official page here .