If you are considering a carbon cross fork, I just purchased the Winwood Dusty for $141/free shipping. I'm only 6'1"/185 lbs, so I'm not sure if I'm below the line of concern for catastrophic failure. I think carbon forks these days are built pretty well, but other Clydes may differ in opinion.
If you're talking $270 for all of those upgrades together separate from the bike, let me know where you find all of that stuff for that price. If it is $270 for components on the better of the two bikes bike, then take the upgrades. Sora->Tiagra is the big upgrade level for Shimano components.