You’re right, they’re different. I’ve got both and the Reba is miles plusher and nicer than the SID to ride. However my Reba has dual flow rebound and is dual air so it’s set up with a bit more air in the negative chamber which makes it a better small bump fork at the expense of outright travel.
The SID is great as a race fork, i’ve done long quick rides on it and it’s fantastic for that but for a trail fork I think the Reba wins hands down.
I don’t know if this is a lot to do with the dual air though and the extra setup tweaks that gives though. I’m hoping that when I can finally get my hands on the 32mm tokens I can get the SID a bit better by running less air in it, it’s quite harsh now.
Also how old is the SID? I think the last year of dual air (2012?) is extendable to 120mm, combined with a bump in neg pressure you might be able to improve things before splashing cash on a new one.