For benchrest a 30x on up is nice to have. But if you have to look at multiple targets having that much mag can be a pain, narrows your field of view to much and makes it tough to acquire new targets quickly.
I doubt anyone would tell you that a scope in the 4-20, 5-25, 6-24 range is a bad choice for precision rifle shooting. The only reason to stay with a 4.5-14 or less is when the size and weight of it is more important than actually zooming in.
As for focal plane it really depends on what you want to do. Depending on your scope the reticle thickness plays a big part. If I were shooting benchrest @ 1k yards the bushnell g3 reticle is a tad heavy at .06 mils thick. The athlon cronus is way thinner at .03 mils thick. In that particular case the front focal isnt as detrimental with the athlon vs the bushnell. For steel I really dont mind the thickness of the bushnell and may actually prefer it though.
My deer rifle is a second focal 4.5-14, it has a heavy duplex so that I can always see it in low light situations where the thinner duplex would get lost. That said when I draw my own dots on paper my choice in heavy duplex does cover up most of my aim points at 100 yards, for paper shooting the thick second focal plane scope is a detriment.
I just recently bought a midas though as it is second focal and for my 100 yard 22 competition I like that the thin reticle and second focal plane, when zoomed in, it is half the thickness (amoutn of target covered up) of my current scope for it, that will help when trying to hold exactly on the 1/8" center white dot instead of trying to use the outer rings and none of it is unknown distance so the front focal wouldnt really be of too much benefit.
If you want to see a good example of first focal vs second the new revamped bushnell site actually has a realyl neat feature on each scope page where it allows you to zoom the scope and see how it changes the reticle. The last section before the bottom of the page is the interactive thing
Here is a front focal example, drag the orange bar down low and slide it to the right to zoom in.
http://www.bushnell.com/Products/Riflescopes/Elite-Tactical/DMRII-Pro-3-5-21x50/?sku=ET732150ED
Notice how when you zoom in on the scope you also zoom in on the target but that the target and reticle stay the exact same size in relation to one another. That means the what the reticle says is always what the reticle means.
This is a second focal example
http://www.bushnell.com/Products/Riflescopes/Engage/6-24X50/?sku=REN62450DG
When you zoom in the scope fills up the same amount of the image view but the target gets bigger. The reticle and target scale at different levels so depending on where you are at in your zoom range the reticle is actually showing a percentage of the true values. 1 mil at 10x is actually .5 mils at 20x and 2 mils at 5x. twice the zoom, half the value.
SO mull over exactly what youre wanting to accomplish and then we can more accurately guide you.
