Sorry, but I also need to comment this post...
We will all NEVER know what exact performance you can get out of SL8 and X68. It can simply be due to personal oppinion / feeling (which is not relevant) OR because we do not know X68 numbers OR we are simply shit riders that can't even use full potential of bikes.
I would also like to hear your arguments comparing X68 to SL8 as day and night. In what ? how do you back this comparisson up with some non-personal facts?
If we blindfold you, and put you on X68 with S-works stickers...are you sure you would reckognize which bike is it? =)
So, there are many of us that can absolutelly agree that X68 frame (700 USD) and SL8 (4-5K€) is more than comparable with ride feel.
I've used the original SL6, SL7, and SL8 for 5 years, and since November I've been riding the X68 on the road, but mainly on rollers.
The difference is night and day.
Even just hitting the two frames with a coin.
You'll notice it on the road at the first bump.
On high-speed descents.
If you try to brake the front wheel from a standstill and push back and forth, you'll see a pronounced flex in the X68.
On rollers, if you sprint, you'll see a pronounced flex in the bottom bracket area.
So the frame LOOKS LIKE a TARMAC SL8... it's not.
Some people say: my friend races with it and it goes fast... OK, I believe it, with a Tarmac it would go even better.