ATM Eypiece correlation to magnification

["Andersen, Clark R." <clanders@utmb.edu>]

Once upon a time I had a 6" reflector scope, about F/5 or F/6, I think (a
Criterion Dynascope).  With that telescope a 9mm FL eyepiece provided a
pretty substantial magnification; in fact, seems like I predominantly used a
12.5mm for planetary work, zooming in later with a 9mm and 4mm, occasionally
doubling with a barlow (enough to see Galileo Regio on Ganymede, on one
occasion of particularly good seeing).  About a decade ago I sold that scope
after leaving it in the garage untouched for a couple of years (for a
ridiculously small sum...silly of me).  Recently I felt the urge to get back
into observational astronomy, so I built myself a 4 1/4" F/4 reflector and
picked-up a 9mm eyepiece, thinking that would probably be about right as an
intro to planetary observing.  What I find is that I've created a wide field
telescope... the 9mm yields about 3/4 degree FOV, which shows craters on the
moon and star fields nicely, but is not very good for planets.  I'm assuming
that the shorter F ratio is the problem, and looking down the line at the
next scope (might even grind the mirror for that one).  Based on experience
thus far, and what I've heard following this group, I'm guessing that what I
need for decent planetary observing is a long F ratio scope, at least F/6,
perhaps even F/8 or F/10 (an 8-12" parabolic mirror would also be a plus).
The only down side to long F ratio's that I can conceive of is reduced
portability.  Seems to me that it would simplify mirror grinding and
figuring considerably as well.  I'd appreciate any comments/advice before I
commit myself :)