That's interesting about the electron firm envy being straighter for you. I got the proto electron glow and I love it! I had misgivings about going firm but I guess I was missing out.
I don't know if the soft neutron is more stable than an eclipse.. I'd say it's a less stable front end, so less HSS but way more likely to hook up at the last 5 - 10 percent of flight. It's just like, I'm done time to fade out, always. It always hooks up.
Soft neutron is a nice ride in the winter. Honestly though I haven't bought many new runs. Just old info haha. Most envy fly about the same, electron being special. If you want less HSS the soft envy is probably a good idea.
But I'm biased, buy more envy's
I have had Soft, Medium, and Firm Electron Envys. Neutron, Plasma, Eclipse, Proton, and Soft Neutron Envys...All of these being 172-174g.
The Plasma I had was stiff and was, without a doubt, the most overstable Envy I have thrown to this day. Based off my experience with the Eclipse Insanity (Thunderbird levels of stability) I assumed the Eclipse Envy would be the most overstable but it was actually more in line with a freshie Electron Envy.
I've not thrown a squishy plasma but this is my general experience with Envy's...
Plasma > Soft Neutron > Neutron/Proton > Eclipse > All Electrons
the difference between any of these plastics is not much. i.e. the difference between Plasma and Soft Neutron is not a whole lot but Plasma compared to Electron is a larger, more tangible, difference.
I could have gotten an odd Plasma. I could have also gotten an odd Eclipse too. Because I immediately returned my Eclipse Proxy because my Eclipse Envy (a little beat up now) flew almost identical.
Bottom line I guess is to try some out or just go with what you want to have. You can't go wrong with a premium/base combination. I personally like the feel/grip of Neutron and the 'give' of the Soft Neutron so I almost exclusively have those. I have a SN Envy, SN proxy, Firm Envy, and sometimes I throw my soft electron super beat super flippy Proxy in there.
Right now the SN proxy is a bit more stable than the Firm Envy which is pretty beat in...bt that Envy has literally no fade and also almost 0 turn. If I put anny on it, it holds and pans out with enough height, if I put hyzer it flips up to flat. It's a special disc but I do hope the SN Proxy will get to that point soon because the 'sweetspot window' for base plastics is inversely proportional to the amount of trees hit...and that Electron Envy is right on the hairs edge of exiting that sweet spot.