I can't speak for the 350, but the delay is horrible with the Pro HD. There is 3 or 4 second delay between button press and seeing it. I use quick skip.
I second this, 30 second skip is the best way, otherwise you have a hard time getting stopped at the right location.
Hopefully one day Slingbox will integrate with the TiVo using IP controls instead of IR and it will improve, along with decreasing the lag.
Note: If you have your Slingplayer set to Control mode on the PC app(they don't support any longer) this isn't an issue, but performance is horrible in my experience.