I'm not sure 250 is possible. It relies on modulation quite heavily (you can hear obvious chorusing in the tail), so not sure how well Nebula captures that. Would be nice to check and, possibly, be proven wrong on it, though. Meanwhile there's very good EMpTy250 from Empty Room Systems and apparently SKNote develops 250 emulation too.
Sanctuary is loosely inspired by the EMT250. With the Size set to 0% and the Attack set to 0%, the early reflections should be similar to an EMT250. There are a LOT of differences with the EMT250, though, the big one being that Sanctuary is not a "constant density" algorithm. The initial tap pattern and spatialization is similar to the EMT250, but the echo density builds over time.
In addition, I am using a somewhat different modulation technique than the EMT250. The examples of the EMT250 I have heard have a preset chorus depth, and totally randomized modulation. This works well when you have a maximum decay limited to 4.5 seconds, but when you increase the decay, and have modulation rate/depth controls in there, the randomized modulation can sound seasick. I used a "detuning" modulation, that preserves the pitch of the decay better, and also adds a lot of stereo width (the latter is due to a modulation technique I've never tried before, that I'm pretty excited about).