I already did it. I have two Hellcats and I bought a 2019 Shelby GT350. Paid 55900 OTD fully loaded. I've never been a Ford guy or a mustang guy but I have always loved Shelby. The how it happened is a lil interesting. I was at a Chevy dealer literally trying to make a deal on a ZL1 1LE when my buddy called and said he just bought a GT350. I told him where I was and he stopped by. I saw it, heard it and sat in it. I knew I was in trouble. Then I drove it......holy hell. That car feels incredible and it feels very special. I was always afraid coming from a Hellcat it would feel slow. It absolutely does not. It lacks the low end torque but my Gawd does it make up for it. That flat plane crank V8 sounds like nothing else on earth and the gears are so long reving past 8k RPM. The grip is other worldly. I went home did some research, realized I'd had blinders on and started my search.
Found a 2019, Ford Performance Blue with white stripes 3 months old with 1600 miles on it. Bought it the next day. This tastes bad coming out of my Mopar mouth......but I'll say it here...it's my favorite car to drive. It so engaging with that manual and if feels just incredibly special. The motor is hand built by one person and it's on of the few if not the only 500+hp naturally aspirated motors left in existence. The more I learned about the car and it's development the more I fell in love. I would recommend a 2019 for the upgrades that I won't belabor here but very much worth it. Ford Performance made a huge fan out of me pretty quick and I don't give a damn what anybody says.
Hellcat faster in a straight line? Absolutely. It's not even close. The Hellcats have so much torque and ungodly power. I LOVE both of mine. Charge Hellcat I maintain is the best daily and sedan on the planet. Challenger is the best muscle car on the planet but my recommendation is quite enthusiastically for a 2019 GT350. No need for the R in my opinion. The updates for 2019 narrowed the gap so much it's not worth it.
My other votes for the record would be a ZL1 1LE. There are several new 2019s in the very low 60s with lightly used in the high 50s or a Backdraft Racing 427 Cobra. ZL1 is a monster with incredible straight line and track performance. Driven it....love it...still want one. Shelby just had something it didn't. Cobra is a classic, open air, crazy power sound and grip. Amazing to drive and a very unique experience. It is obviously a sunny day only car though and lacks any kind of modern safety features...if you care. My wife does but I'm working on her.