looking at trek and gary fischer... need advice!

[Yelsel]

Your weight has nothing to do with it; you could be twice the weight and not have a problem on either type of bike. (And you are not overweight - your BMI is normal, and you are definitely in the lower percentiles of weight / height.)

The two typical measurements in a fit system for standover are inseam and torso. Measure your inseam by putting your feet 6" apart, jamming a thick book in your crotch, standing against a wall to level the book. Ideally get someone to help you with the measurements -- measure down the ground for inseam. Measure up to the dip in the clavicle bone for the "traditional" torso measurement -- a T-square, level, or plumb bob helps with these measurements.

If your inseam:torso length is between 1 and 1.2, then the "fit" guide will suggest a mens/unisex top tube length.

A couple of caveats, which kind of cancel each other out: the *important* torso measurement is actually to the middle of the shoulder joint, not the dip in the clavicle. You don't use your torso above your shoulder joint for reach! Per Gale Bernhard's research -- she has this in all her books -- men and women have the same average effective torso length, while men have more distance between their shoulder joint and clavicle. So this suggests that women on average just need smaller bikes, not ones with especially short top tubes.

Riding style really has the most to do with a comfortable top tube length, though! On average, women seem to prefer a slightly more upright / less agressive angle than men, which might have to do with women's hip geometry and/or narrower shoulders on average (based on the way I ride, I'm voting for the latter). So shorter top tubes work better for a lot of women... so shorter top tubes are the answer for a lot of women, though ironically not because of actual (average) physical geometry differences in torso length.

I have a 32" inseam, my inseam:torso ratio is 1.1. My arms are slightly on the long side ("positive ape" of 2 inches -- 2 inches longer from tip to tip than my height). I do have wider shoulders than average for a woman, which I think might be an underappreciated metric for preferred riding style. My hands are large enough to handle "typical" bike components - I take a small / medium in men's gloves (I'd still love the short-reach STI levers, though). When I was looking for a bike in 2005/2006, women's styles in general didn't go up to my size (54-56 in women's); I rode a Terry but all the other bikes were men's. Just by feel, the Bianchi felt the best -- I took it home stock (after a real fitting) -- Bianchis have shorter top tubes than average for men/unisex, which is why I think these bikes are really popular among women that don't ride a women's specific bike. (They also effectively don't have women's bikes -- two bikes is not a line!).

Trek and Gary Fisher have some of the longest top tubes in their men's / unisex. On paper the women's should fit me better, though the top tube is a bit shorter than what I ride now. But women's bikes typically get a lot of their top tube shortening by steepening the seat tube -- which puts you closer to the pedals, which is not what you want for longer legs! If you move the seat back, then you are lengthening the cockpit anyway. I'm not knocking these manufacturers at all -- but neither geometry works well for me, so it is good that I know that. (I have a Giant Anthem on layaway, which has a very similar equivalent cockpit length to what I ride now.)

Instead of top tube length, a better metric is cockpit length - from your butt to your hands; this is getting to be more common for mountain bike manufacturers to include because frame styles vary more widely. I know GF reports this, I don't remember for Trek. They report the "stock" cockpit length, and minimum and maximum (moving seat fore/aft and swapping for typical stem lengths).

The bottom line is ride bikes from a lot of manufacturers, and find the one that is most comfortable for you. All of the major manufacturers have very similar frame performance, weight, and components at comparable non-elite (aka sub-4k) prices. If you absolutely hate the component line stock on the bike, you can generally swap out comparable parts in a different line for little to no cost on a new bike.