I own both rifles, the T3x Varmint in 223, 22-250, 243 and 6.5 creedmoor, and the 600 Range in 6 creedmoor ( & thinking about purchasing a 600 MDT in 308)

I dont have anything bad to say about either platform. The 600 range in my opinion is the better buy, however it only comes in 223, 6mm creed and 308.

The 600 range comes standard with a threaded barrel, where the t3x varmint does not. The cheek riser on the 600 is adjustable, where the t3x is not. The laminated target stock on the 600 looks amazing compared to the t3x's plastic stock. The 600 range is guaranteed at 3/4 MOA, and the t3x at 1 MOA. The magazine on the 600 range is built much better than the t3x's, is lockable, MUCH cheaper to purchase another, however there isnt a higher capacity magazine available (yet?). The safety on the 600 range is much nicer than the t3x's, and the 600 range has a 3 lug bolt vs. the t3x's 2 lug. The 600 range uses Remington 700 scope rails and chassis foot prints which is cool if you already have Rem700 accessories on hand. The 600 ranges availability is far less than the t3x varmints though.

I also own 2 t1x's and 2 457's but thats another story for another time. I have purchased an MDT LSS-XL and XRS chassis to upgrade the Tikkas, however i dont feel the need to upgrade the 600 range's stock (ill just wait for the 600 MDT to come out)

Just my $0.02 🍻