I guess I look at it differently. If the trade wasn't of any interest to you, you would not be asking, correct? If it is something that interests you and you wind up "total cash neutral" or better, than I would do it. I see some 625 JM PCs on Gunbroker so it is not like you cannot find another if you end up hating the Sig. I would just think about how the Sig market is in your local area. Some areas are Sig areas, some are S&W areas, some are Kimber areas. You get a good feel for how many of a brand and types are in an area from Armslist. I am not promoting that site, I am simply saying it is a good barameter of what brands are well represented in your area.
If you look on GB, NIB for the two, the Sig is actually more. You have to judge in your local market what the used price is for the two. All boils down to if the Equinox is something you like and want to have. I have tried two of them in the last couple of years and I dont like that model cause the grips are so chunky and I have small hands. However, throw a set of E2 grips on them and now I can clean out the 10 ring