I have had both.T3 was very good shooter, T3x is great with some improvements over T3...Sako/Tikka tells you all about it, so I will not bore you.
The A7 has bit ‘bigger feel’, if you like that, then it may make a difference.The trigger and barrel are likeother, more expensive Sakos they are great.The A7 Roughtech pro is a very different from the T3x....stock is solid, feels good, and has full aluminum bedding block with aluminum exoskeleton in the stock....means that it will shoot lights out, and stay lights out, until you sell it or pass it down.It shoots like many custom rifles, but it ain’t lite.
If you buy new from a store, with retail ,or even discount ,plus the regular tax, then the T3x is the no-Brainer over the A7;however, if you can find an almost new,A7 Roughtech pro, then that is the rifle to get.They are excellent rifles, especially if you get one at a T3x or lower price....I did.
Only caveat-
Unless you are looking for an ultralight mountain back pack rifle...then get the T3x in 270, 6.5 Creedmoor more, etc. and you are done. There are none better for the price/weight even if you pay 2k more.