You can't shift from the drops with Sora. Deal killer for me. Microshift/Nashbar/Forte (Performance) seems to get good reviews and is very cheap. Some Performance bikes come with the microshift group and it seems it's fully compatible with Shimano derailleurs and cassettes.
If it were me, I would buy the Sora bike, switch the drivetrain for your old Ultegra (shifters and derailleur), put the Sora drivetrain on the old bike and sell that. Old Ultegra is much better than new Sora, I suspect, and you still have the Sora drivetrain if you want it.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter