what's your A setting on axisspec line of your X axis in your wincnc.ini? That is your acceleration for rapid and feed. If it's, say, a800, that means if your feed speed was 100ipm, it would take 1/8 sec to reach 100ipm speed. If it was a100, it would take 1 sec to reach full speed. Adjust that setting and see if it helps. I see no reason why your G09 should be lower than 5, as it can make it choppy going around curves. The higher G09, the smoother going through curves.
Also, you can add an F number in the axisspec if you don't have it. That give your feed speeds a different acceleration than rapids. Like you could have a400 and f200. For simple rapids it would take .25 seconds to reach 100ipm, and when running the actual feed cut, it would take .5 seconds.
it may help you. (ps, I have different router, but have had to tweak these settings for my router)
the accel setting at the top, I believe sets the velocity jump increment when accelerating. It doesn't set the actual acceleration. However, if you set it super low, like 2, you will force it to take so many velocity steps that it may trump your acceleration setting. It should be fine on 50 or whatever.