I installed the DXI 651 Polks.
Better volume and base.
Best utilizing these with an amp as the oem system doesn't have enough umph to bring them to their full potential. For a speaker only upgrade, they sound as good as oem before distorting, but with 1.5 % more volume.
They are Marine grade, by the way. I also pondered the DB vs the DXI and contacted Polk for an answer. They said they were both Marine rated and the DXI would have clearer highs.
I've had both. They both do best amplified.
By the way, the 5.25's are rated about the same. Think I might throw a pair of these I have on the bench, in. Just to hear any difference.
Did I say amp....
Jim