I have a iic++ Simul class (105 transformer) and a red stripe mark iii Simul class, both with Sylvania 6l6/ el34's and 8th gen Chinese preamp tubes.
I had the ++ first and of course it's amazing. Got the mark iii recently. Bought it for it's hardwood head shell and original Sylvania power tubes. I planned on selling the chassis to recoup some of the funds I spent on the amp and find a factory iic+ to put in the head shell and use the power tubes in. I plugged into the mark iii and was blown away. It sounds absolutely incredible. Aggressive, tight, tons of gain..and it's a 3 channel amp. It's VERY close to the iic++. I cannot now really justify spending $3k or more on a factory iic+, or any iic+, after playing the mark iii. It's really, really good. I don't know if I just got a really good one, if the original Sylvanias are making the difference, or what. But it cops the tone and feel very closely.
For the collector in me, I'm still tempted to get a factory iic+, but as far as tone, the mark iii is just too close...