2.10" with a VMax 110 over 1680, 19gns should put you at about 1900 fps from a 16" barrel and about 90% case capacity...you can work up or down from there accordingly.
I wouldn't recommend seating the VMax's any longer than that because 2.1" already puts you at only ~4.5mm seating depth assuming a 1.355" case.
Just shot some today and got two 3/4" 10 shot groups at 100y. 18.5gr of H110 got me an average of 2345fps. COL was 2.075. Upper as a factory Noveske 16". Cycled well and ran clean.
1680 is great for sub loads. I use it for both 220 and 150gr sub loads, but I still use H110 for supers. I don't know that you will get as much velocity out of 1680 when you load it supersonic.