With your 6sp cars the 4.10 gears will be fine. Because you have a 6sp and the ratio is so wide you can cover the gear change. 1st gear will go by really quick... But your 6th gear has such long legs that the car will still easily get up past 150mph.
Use the gear calculator tool in the Tools section of this site. Or go to Richmond or one of the other gear vendors sites. They have calculators for this.
With a 3.54 gear in my auto trans and running in OD I could still get to 150mph. OD ratio is 0.7. My 275/40-17 tires have a diameter of 25.7".
The formula looks as follows:
RPM = (((RE Ratio * MPH) / Tire Diameter) * 336) * OD Ratio
I have heard that 4.09's will make the car's top speed go from 5th gear to 6th gear (the stock 6 speed top end is in 5th)... However, I haven't done the math... It gets complex here... It comes down to how well your car can run in 6th gear.... basically what needs to be factored in are: how much HP your car has(and at what RPM... how much HP do you have at High RPM?) the weight of your car, the drag coefficient, the final drive ratio, tire size.... What you are trying to find out is if the car has enough horsepower to move itself in 6th gear at high speed... if it can't, you have to figure it out for 5th gear