I did a side-by-side comparison of the Edmund 4" with the Pentax 85. Because of the different focal lengths, I could only get close to the same magnification, with different eyepieces. The Pentax gives a perfect star test, which was a good reference for the Edmund, which is still showing a slight bit of overcorrection. The Edmund's additional aperture, however, was making up for the slight loss.
On Regulus, the Edmund showed more CA than the Pentax. At 47X on the Edmund and 40X on the Pentax, Castor was equivalently split. The extra aperture gave the Edmund an advantage on deep sky. M13, M81/82, and M57 were similarly resolved in both, but brighter in the Edmund. That made it easier to see stars to the center of M13, but the Pentax had more of that feeling of the stars being like fine dry sand, versus a wet sand quality in the Edmund.
On M81 and 82, there was similar resolution of the structure, but the added brightness in the Edmund made it easier to see, with less use of averted vision. However, the Pentax was able to go to a wider view that provided more context, while the widest view in the Edmund had them closer to the edge of the field.
With the ring nebula, which is brighter, there was less of a difference at lower magnifications, but the Edmund could go to higher powers and still have it stand out strongly against the background.
Lastly, I was able to see Alberio for the first time this season. In the Pentax there was a bit more of that sparkling quality that comes from having more of the energy concentrated in the airy disk, especially in the secondary. With the Edmund, the stars were tight disks, but not with as much of the bright point in the center. Of course, the extra aperture made them brighter overall.
I will be very curious to continue the comparison on the Moon and planets. The Pentax gave stunning views of Venus last year, and I'm hoping to use it when Venus and Mercury are in conjunction later this month.