An 8" SCT can beat a 5" APO, a 5" APO can beat an 8" SCT, an 8" SCT can match a 5" APO...Location and Seeing are the primary culprits. All the other variables have their effect too.
I've had 80, 90, 100, 130 and 140mm ED/APO refractors and 90, 130, 150, 200 and 280mm MAK/SCT's. Compared them head to head many nights. There were nights the refractors won...there were nights the SCT's won. My 4" TV Genesis has beat my C8... My C8 has beat the Genesis. My AP130GT has trumped my C8/C11...My C8/C11 has trumped my AP130GT. My TEC140 whipped my C11...My C11 has whipped my TEC140. To make any other claim or state absolutes about this topic, is simply folly. There are indeed too many variables to account for. In general I find that I need at least good seeing conditions and weather to allow the sct's to strut their stuff, but strut they can. So too can the refractors in average seeing conditions and less. I will always have at least one of each type to compliment, not compete, with each other.
I think you need a C5 to round out your SCT's