Here's a screenshot from the SpaceDev site which shows an animated version of the Dream Chaser on top of a rocket, presumably an Atlas V.
Was the SRB ever in the running?
As for dimensions, the SRB and the Atlas V are very similar. Performance wise, well, I don't know. The SRB is supposed to fire for about 2 minutes. But it generates a lot of thrust. Both SRBs in the Shuttle configuration provided 83% of the liftoff thrust, but only 60% of the mass.
What that would mean in terms of altitude and velocity for a 25,000 pound craft, I can only guess. The shuttle weighed 10 times as much. A single SRB just might be enough to get to orbital velocity and altitude. But could it be recovered?
The Ares I was designed to send the Orion into orbit. The Orion's mass came in at twice what the Dream Chaser's. With far less mass, all the Dream Chaser may need is just a little more boost from its own onboard rockets in order to reach orbit. I'm not 100% sure of that, though. Maybe a lot less than 100%.
This isn't a flyable rocket, but it could all be 100% reusable, if the SRB could be recovered in good shape.
Thanks for coming by and have a great evening.