If you're right handed, the Speedfeed stock won't be a problem as the shell holders on the stock's left-side are placed lower than those on the right-side.
If the Speedfeed shell holder stock is still of concern, Mossberg does have a 20" 590A1 with a regular synthetic stock, model
51663.
I have no experience with the SPX model, but don't see any particular problems with a ported shotgun barrel.