fall planted cover crops that are ready to harvest early spring. zone 6a/b.

So this last year I planted some winter wheat and hairy vetch around early October as cover crops. The wheat didn't seem all that happy about growing here. The vetch however grew awesome on my newest hugel. I would like an overwintering cover crop that I could harvest early to mid April that would provide a lot of straw/mulch. Just wondering if anyone else from a 6a/6b zone has had any luck with anything that meets this criteria? Been doing a bit of searching but not having much luck. If I can get a seed harvest from it that would be a huge plus as well. Its about .25 of an acre with full sun and decent moisture that I'd be covering. Ill gladly experiment next fall but if anyone else has more experience and wouldn't mind sharing it, I'd love it!

Straw type mulch takes more maturity than you can achieve by April.  Flax makes a very tough straw that they make linnen out of.  It will stay intact over the winter as a straw mulch if planted thickly from my experience last winter.  If you can plant it as an under crop for tall crops and then it can continue to grow after the crop harvest until flattened by snow you will have a straw mulch when the snow melts.
I am in zone 7  so I usually get one snow event in december and another in January and the snow only lasts a day or two. but the black flax that I bought in the bulk bins did the job and now weeds came up in the two long strips that I planted it.

I'm in about the same zone and I too am growing hairy vetch- but I don't think it'll be ready until May. For mulch I cut some reeds and petennial grass from around the area.

Vetch is starting to flower now and the winter wheat has put on heads..it'll work but I think Ill try barley and rye this year to see if they are ready sooner.