If the SL7 and SL8 are the ‘one bike to rule them all’ with no Venge then the Tarmac should be compared to the Madone and Propel as well as the TCR and Ultimate. My understanding having not yet ridden a SL7 or SL8 yet (my Pro is still in the box) or any of the aforementioned, the Propel is positioned more closely, as an all round racer, lightweight with aero like the Tarmac now, would also like to hear Super Six comparisons.
I don’t know if Canada will get an Ultegra spec of the Propel this year but the Force spec (Advanced Pro 0) is significantly cheaper than the Tarmac Pro (I got an ambassador discount and the Giant is still cheaper at retail than my discounted Tarmac lol), with the Madone SL 7 its closer but still ~$650 cheaper than what I paid for my discounted SL8 Pro. I expect the SL8 is lighter than both on paper, I wonder how they compare in ride quality though, handling, compliance, etc I like that that the SL8 can clear 32s and has a threaded BB, which are pluses over the Propel in my opinion.
I’m not looking for comparisons that will make me regret my choice, hopefully (especially once I build it and start riding it) I will be content with my bike for a few years but as someone who hasn’t ridden a lot of different bikes its nice to understand how different models compare.