I've had the same good intentions, and finally found a way to put it to the test last year. It was a miserable failure by most accounts.
Too much moisture is our limiting factor most years and a thirsty cover crop in the spring should be a good fit.
We seed as soon as the ground is fit in the spring, and most harvest is done long after freeze up, so options are limited. We were considering doing some organic, so I underseeded a couple partial quarters to a blend of clovers at the same time as the barley, with the intention that it would be a plow down cover this year, or better yet, cow feed then plow down.
Big dump of rain immediately after seeding, then basically didn't rain again all summer, or this spring/summer again. So the higher ground didn't amount to anything, lower ground did very well, much better than the barley which drowned out right after seeding. Silaged the clover in the low spots.
By this spring, we had abandoned( or postponed) the organic idea, so the plan was to leave the clover growing and fixing N as long as possible, green seed into and terminate it. When conditions turned from wet to desperately dry almost overnight this spring, we terminated the clover as soon as possible to save some moisture, and seeded canola into it shortly after.
The lower areas where the clover was lush had very poor canola, there was just not enough moisture left.
Roundup alone wasn't as effective as hoped on young clover either.
Need a lot of moisture to make it work, which we normally get, but 1/4 of normal this year, and nearly as bad last year( got it all at once) doesn't lend itself to cover crops.
Les Henry had an article about this recently:
I will try again, 1 in 100 year droughts don't happen very often...
I think the only really effective way to make it work in our short seasons and still be profitable is to have enough livestock to make use of the cover then dedicate a year just to the cover crop, perhaps seed a winter or fall crop into it after.