I thought the rule was 6-1 ratio for safe flite

I've heard a variety of "rules of thumb". The truth is, there are a lot of things to keep in mind. A stable, proven rocket with a decent length rail on a calm day can pull of 3:1 or 4:1 without difficulty. Most rockets can do 5:1 or 6:1 on an average length rail on a calm day, and fly beautifully. Other rockets are more questionable (see below for more detail than you ever needed to know), and need a harder kick to be stable. On a breezy day, go at least 10:1, with more like 15:1 if the winds are higher (but still within safe limits).

The speed a rocket needs for stability is variable, but as a general rule, it depends on three things. First is the distance between the center of pressure and the center of gravity. The smaller this is, the faster a rocket will need to be going to be stable. Second, it depends on the force the fins will develop when at a given angle of attack. For the most part, you can approximate this by scaling it with the area of the fins. Highly swept fins will be slightly less efficient at this, and low sweep will be more efficient, but that's a smaller effect. Finally, it depends on the moment of inertia of the rocket in the axis perpendicular to the tube. If you have a ton of noseweight and a heavy motor, the moment of inertia will be higher. Also, if the rocket is longer, the moment of inertia will be higher. This means that it will take a greater restoring moment to cause the same effect, and it will (effectively) slow the ability of the rocket to correct itself. If your rocket is stubby, lightweight rocket with 2 calibers of stability and huge fins, it will need much less speed for stability than a long rocket with a ton of noseweight, small fins, and a static margin of 1. My AIM-120C AMRAAM is a good example of a rocket that needs a very high speed for stability. It has 10 pounds of noseweight and uses large, heavy motors, and it only has about 1.5 calibers of stability. However, its fins are not very large, and include decent sized canards. Because of this, my AMRAAM requires a much, much higher velocity for stable flight than would a standard rocket. On the other end of the scale is something like a Big Bertha. It is lightweight, has huge fins, and a very large margin of stability. As a result, it will happily fly at very low airspeeds with perfect stability.

In addition, the entire paragraph above is dealing with the airspeed required for safe flight. Once you have figured out whether your rocket needs average, above average, or below average airspeed for flight, then you have several possible ways to obtain that airspeed. You get the same airspeed with a fast burning motor off a short rod as you would off a long rod with a slower burning motor. It's all a balance of the factors required for safe flight, and it isn't quite as simple as many people think.

This is why any "4:1" or "5:1" or "6:1" rule is just an estimate for an average rocket, and not always applicable. In general, I would go with at least 8 or 10 to 1 for an unproven design on a first flight, as the factors above could affect the way it flies significantly. Once it has proven stable, and if it doesn't appear to be excessively wobbly off the pad, you can go for the slow, majestic liftoffs.