6" cans on a 8' ceiling look just fine. If you want to, you could consider 4" cans for asthetics. The cost is higher.

Have you looked at CREE LED lights? The LR6 lamps are not glaring and provide quite a wide spread of light. The CR6 will be available soon at a lower price point.

First you have to know what the inulation is over your ceiling. You will be limited to the wattage for insulated ceilings unless you are using batts and not blown insulation. My most favorite light solution in a kitchen is the deep alzack refelctors (deep)They use regular A lamps and if you purchase good quality ones, they spread the light out wonderfully and have a great cut off anlgle which controls glare. IF you buy cheap specular trims and the bulbs sit low in the trim, it is very bad. Juno and Lightolier both make deep alzack trim. Not sure about Halo, haven't sold them in a while. The very best ones in my opinion were made by prescolite but they can be hard to find. On an 8ft ceiling you will not need more than 75 Watts. Another tip has to do with the bulbs. While I am a big proponant of 130 V long life bulbs, they are slightly more red than the 120's. What works the absolute best in a good alzack reflector is a soft white, sometimes called reader white bulb. Use these with a dimmer to extend the life of the bulb and adjust the dimmer whenever you don't need all the light. Recessed lighting can be confusing and with all the bulb changes coming, even more so in the future. The LED bulbs that were suggested are great for energy savings and also they never burn out. I still find them strange however for lighting kitchens and the deep alzack trims are not designed for anything but an A lamp.If you buy a reflector trim and then use either a Par or R lamp, you wasted your money. As to spacing, IF you are lighting any room other than a kitchen then 4 deep alzack reflectors with 75-100 watts iis fine for general lighting. Kitchens are more comlicated since we need both general and task lighitng. I would use 6 if that room is a kitchen making sure that you have all the work areas covered. In a kitchen if you place the recessed cans 18" from the wall, the light will fall on the counter surface and also illuminate the cabinet doors and inside spaces when open. Don't forget to have lighting over any island work space. Use undercabinet lights under your counters. That is a good application for LEDS. The Alzack refelctors will cover about 6 ft of area of that 8 ft ceiling. On higher ceilings the area of light increases, but the footcandle level will be lower on thework surface. Tall ceilings need 100 Watt A lamps but 8 & 9 can usse 75 watt. Whatever you use, be sure that it meets you local electrical code. Don't be bullied into just whatever the contractor likes. Sounds like you found a good showroom where you were getting good information. Perhaps you could purchase the recessed there, where you may be getting professinal advice. Remember most Electricians are not lighting designers!

I do not like general illumination from the recessed cans in my house. In my kitchen, I have 4 cans, poorly placed, but I do have to use them sometimes when there's not enough light from the 2 old undercounter fluorescents. I unscrewed the one that hits the top of the fridge, but found I needed the other 3. They are too bright and harsh though.

I would never want to put them in a bedroom or in the living room. I prefer indirect lighting hitting the walls or ceilings, from sconces or wall washers, with reading or task lamps in specific areas. The overhead light is too bright, harsh, glaring, and creates shadows.