Sound of SED Winged C KT88 vs. SED Winged C 6550's

Curious as to what if any sonic differences I could expect in comparing the SED KT88's vs. their SED 6550 counterparts. I've researched the forums quite a bit over the last month or so and even asked the question to Kevin Deals gatekeeper @ Upscale Audio... his response was that there was little to no sonic differences between the two.

My amp is a McIntosh MC275 MKV, currently using the stock McIntosh KT88's, which I've been told by Audiogon's Nsgarch, are SED KT88's.