1-7" is fine. Yes, at ~1.33 the Sg is marginal on paper for the Berger 90gn VLD, but Miller generally understates the real Sg for long HPBT type bullets. In fact, I used to shoot the 90gn LRBT which is only marginally shorter in a 1-7.5 inch twist barrel at only 2,650 fps with great results to 600 yards at least. Experience showed that the originally recommended (by Sierra) 1-6.5" twist barrels usually didn't work out too well.
Twist rate is only one factor though. My understanding is that the Savage 12 FTR is short-throated for 90s. if the bullet has to be seated too deeply in the case you won't get acceptable precision, and your velocities will be severely constrained. In a properly throated 30-31 inch barrel you should be able to get 2,850-2,900 fps. The risk is that having the barrel throated out a bit, you turn it into a one-bullet rifle degrading the performance of 80gn class bullets.
Viht N150 and N550, H. VarGet, Alliant Re15 work well but N550 and Re15 are temperature sensitive and it soon shows up in the little case. AR-Comp which is basically a treated and temperature insensitive version of Re15 might work - can't say as it's not available in Europe. (For fellow Brits and colleagues in the rest of Europe, I suspect Nitrochemie's Reload Swiss RS52 is going to be the powder for heavy bullet long-range 223 with 80s/90s - I'll see once the weather lets me do some testing.)
With 90s and L-R use of the 223 Rem, everything has to be perfect - Lapua match brass with a clean-up neck turn and batched etc, bullets batched, powder charges with tiny weight variations (0.1gn = 10 fps MV change; I worked to plus or minus 0.02gn on lab quality electronic scales, that's plus or minus a single Re15 kernel, for my GB League comp ammo), every cartridge identical in case-head to bullet ogive measurement. Even then it is prone to produce a few shots with poor elevations. I tell people who're considering this path that it's a hard and often frustrating one.
Ifr you want good performance and less hassle, try the 80.5gn Berger BT Fullbore first and see how you get on with it. It can be driven to 3,000 fps plus and is easier to tune for consistent performance. It will perform well at 1,000 yards in the right outfit if carefully loaded. Many users never liked the 90gn VLDs from Berger and JLK and the 90gn LR BT from Berger was their bullet of choice - it was withdrawn a couple of years back and you'd have to be lucky to find any now. (That is another issue of course - depending on two bullet models for an optimised 223/90 rig compared to the vast choice of 308s for 308 Win.)
Get it all right though, and the 223 is a joy to shoot in an FTR weight rifle.