I'm not sure what you mean by "Specs".
The Kia Optima competed in the Pirelli World Challenge from 2012-2015 in the "Grand Touring Sport" "GT4-esque class, below the "Grand Touring" class which was eventually homologated to GT3-only starting in 2015. The Kia competed alongside unhomologated Camero's and Mustangs, but there were Caymen and Aston Martin GT4's in the "GTS" class as well, so I guess that shows about what pace the Kia had.
Today, IMSA and SRO both have TCR series in the United States (IMSA has the Michelin Pilot Challenge, SRO has the TCR-Cup). The Audi directly competes against Velosters, Civics, Alfa Romeos, etc. In IMSA they share the track with the higher "GS" class which is made up of GT4 cars. That said, despite the GT4 "GS" class being the faster cars, the Audi's did show an almost equal pace in the 2018 IMSA SportsCar Encore which was the debut for the new Audi RS3. The Audi's managed to menace the GT4 "GS" cars for a good bit before the FWD configuration eventually burned away the tyres and they fell back a bit.
I believe the cars entered the Encore un-BoP'd and have since been BoP'd, but it doesn't look like a giant change. When "TCR" returned to Sebring in 2019, the Audi's finished 2-3-4 with a fastest lap of 1:30.885, the winning Veloster "TCR" went about one second quicker, and the Porsche took the "GS" victory with a 1:27.518.
All in all, the
IMSA MPC results from Sebring were quite the mixed bag, only 4 "GS" cars out-paced the "TCR" class, with 37 total cars on track and BOTH class leaders finishing on the same lap after two hours.
Bottom line, if it were 2015, the Kia would be in the "GS" category, and the Audi would be slumming it in some knock-off "TCR"-esque class like Pirelli World Challenge's old TCR/TCA/TC series. However, if Kia were to bring the Optima back to IMSA in 2019/2020, I'm sure they'd be slotted into the 4-door FWD "TCR" category. Therefore, if iRacing really wanted to BoP these two cars, I see no reason why they couldn't!
Off topic, for anyone interested:
The Encore was a one-off, combining the IMSA Michelin Pilot Challege and the IMSA Prototype Challenge (featuring all-spec LMP3's) for a pretty neat race. As a fan of multi-class racing, I wish this was the actual format, and not just a one-off event.