How large is your kitchen? I think the 4" lights give off much more focused light and 5-6" are more for general lighting. I read somewhere that spacing should be about 1/2 the height of your ceiling - so every 4 ft for an 8 ft ceiling, but that probably applies to 6" cans.

Did you get the type of cans made especially for sloped ceilings? They are more expensive, but the light is directed down perpendicular to your floor, instead of perpendicular to your ceiling. It makes a huge difference.

I'm assuming that you have 12 volt Mr16 lamps.
If that is the case, the rule is the higher the ceiling , the narrower the beam spread.
By using a 50MR16 Narrow Flood, or A 50MR16 Spot, you will increase the amount of light on the horizontal surfaces, but will result in a smaller beam diameter on those surfaces.
The other option is to use 50 watt IR lamp(made by GE and Iwasaki,to name two mfgs)
This lamp will produce the equivalent lumen output as a 75 watt regular MR lamp.
The rule about beam spread remains the same.
If you have 50Par20 lamps or 50GU10 lamps, unfortunately these lamps are not suitable for ceilings higher than 9' in a kitchen

Recessed lights are fashionable, but they're a less than ideal choice for general illumination of any space. They're good for highlighting certain areas. General illumination is better accomplished with surface mount or pendant fixtures, for a blend of direct and indirect illumination.