v4.1.1 Features
Display
VSync (D3D)
VSync now also works with double frequencies (eg 100Hz).
Remark that VSync generally consumes more CPU on the 64bit builds.
Microseconds (Windows)
Use precise hardware counters to time video rendering, if it's not checked milliseconds are used. Microseconds allow emulating the real video frequencies, which are fractional. Timing of display still depends on the hardware and OS (better with FreeSync).
This setting is ignored when VSync is engaged.
BFI (D3D)
BFI stands for Black Frame Insertion. When the option is checked, Steem SSE will update the display at twice the ST rate, one frame will be black, one frame will be the emulated image. It results in less movement blur on LCD screens, but video gets dimmer and some flicker may be perceptible.
This option operates in windowed and fullscreen modes, with or without VSync, but better with VSync. The screen must be set at a high frequency or in FreeSync.
Timing Loop
Steem SSE will start a hard polling loop so many milliseconds before the planned time of blit (video rendering). A higher setting means more CPU use. Generally 2ms seems to be a good compromise (1ms is the previously hardcoded setting). 
However, if your PC is very busy, no matter how high the setting, Steem SSE may lag. The general option Make Steem high priority has a greater impact here.
This setting is ignored when VSync is engaged.
US Border
The normal border size now depends on the TOS language, fewer scanlines for a US TOS, to avoid the black bands.
GUI
ACSI hard drive manager
For Linux too.
Joystick select
New shortcuts that simulate key presses on Num Lock or Scroll Lock for keyboards missing those keys (laptops...).
On Screen Display
Bad jokes
Yes, now it's an apart option!
v4.1.1 Emulation improvements
CPU
Closer to a real MC68000 for BCD operations and for undefined flags.
ACSI hard drive
Some ICD-protocol SCSI commands are now emulated ($25, $28, $2A, $2B), disk image larger than 1GB  are handled.
DMA
Refill FIFO buffer as soon as it's empty when writing to device (no more hack for laser printing).
6301
The 6301 uses an independent 1MHz quartz, not a fraction of the Shifter clock.