Question is pretty well summarized in the title.
If we were to order gears in terms of power provided, where would reverse fall between gears 1-5 on a manual transmission vehicle?
Does it vary by vehicle?
Reverse is pretty equivalent to first gear, for a ratio of around 3.2ish.
If it were any lower, it would be difficult to get started from a stop since the torque just won't be there. If you've ever driven a stick-shift, try starting from a stop in 2nd or 3rd gear and you'll see what I mean.
For example - ratios for my manual 5-speed 2007 Mazda6:
Gear ratios vary somewhat widely from vehicle to vehicle, especially between vehicles with different numbers of speeds, but the reverse gear is always going to be pretty close to 1st for the reasons mentioned above.