You may just find the Gore Power 2.0 3/4 Length Bib Tights to be your most often used pair of bibs. People have different tolerances, but once the mercury starts heading south of 55 degrees, most look to cover the knees to keep the joint and muscles warm. This is instrumental in maintaining an effective and injury-free training schedule. The Power 2.0 Bib Tights 3/4 are the perfect solution, keeping you sufficiently warm without feeling like you're bundled up prematurely.
These bibs use the exact same material as Gore's bibshorts, but in a 3/4 version. That said, it's not strictly a thermal material. They're extremely effective in wicking and managing moisture through a push pull system allowing sweat to be drawn away from the skin immediately and pushed to the outer surface of the bibs increasing comfort and maintaining an optimal temperature. Flat lock seams will keep them from leaving indentation marks in your skin after long rides. Similarly, the gripper elastic on the bottom hem will hold the legs in place without snagging the skin or cutting off the circulation. The inseam length is 19 inches or 48 centimeters, so that it will reach to below your knees but not too far down your calves.
Gore has included their Power Man seat insert to ensure that you'll be able to sit comfortably for hours. Gore calls this insert their workhorse, and they use it for these bib tights because they realize a lot of your off-season training will be constituted by long hours in the saddle racking up base miles. It has an anatomical fit with strategic elasticity and ventilation. How breathable an insert is has a lot to do with reducing any potential for humidity-caused rubbing and friction. With this in mind, the outer fabric (the next-to-skin-stuff) of the Power Man insert is made from a hyper- moisture absorbing fabric.
Gore Power 2.0 3/4 Length Bib Tights come with a mesh insert at your back so that you'll feel well ventilated right where it's best to let some excess heat escape. The reflective flag on the rear of your left side is specially placed to keep you visible to passing cars, and additional reflective logos have been included on the sides of the legs so that no matter from what direction a car approaches, they will have a visible signal to alert them to your presence on the road. They come in Black and in sizes Small through XX-Large.
Here's what I found good: the bibs fit great and the cut is comfortable; Gore's sizing chart seems to be accurate - I'm 5'9" and have a 32" waist, and the medium is spot on; The leg grippers really work well at keeping the bottom hem in place; it's a high quality Lycra they use for them, too; and the reflective tabs stitched into the seams are subtle and unobtrusive.
Things I found less than impressive: the name Gore gives to this particular insert, PowerMan, is somewhat overly ambitious a label to describe the quality of foam used for this pad. I found it less than substantial for medium to longer rides (their OZON insert, however, is top notch); although good quality, the material used for this garment is no heavier, or has no better thermal qualities, than your summer bibs. There is some added protection from cooler weather over the knees, as far as the insulating properties of moisture evaporating Lycra can provide. But I feel the range of use for this bib is limited to those transitions between early to mid spring and mid to late fall, when the variation in temps are shifting throughout the day. You may as well get some leg warmers to fill those gaps and have some thermal bibs or tights at the ready for winter.