Hiya peeps, long time no talk.

I have a pretty basic question regarding optics, if anyone would like to take a stab at it.

I'm going to build an 8 inch Dobsonian this spring and don't really have any way to see the difference between an f4.5 and f6 before I make teh decision to buy the optics kit (http://www.e-scopes.cc/).

Basically, do I need to really worry about the differences in performance between the two, or is there so little difference that a casual user wouldn't notice? IE, will there be much of a difference in color and contrast in Messier Objects between the f4.5 and the f6? How noticeable is the difference in magnification for closer objects like the moon and other planets?

Thanks much for your time!

MrPex