For either rifle, I would get a 24" barrel. I have a M70 and M700, both with 22" barrels. I cannot push my 140's as fast as the velocities you see in manuals or as fast as shooters claim. I do believe that a 22" barrel really drops the velocity of the bullet un necessarily. The Swede is capable of excellent accuracy, have bud's who have long range rifles chambered in the 6.5 Swede. Of course a sporting rifle is not capable of target accuracy, but still, the 6.5 Swede does well.
M70 Featherweight 22" Barrel
143.5 gr FMJBT Swedish 1986 ball. OAL 3.065" 47.4 grs powder average
13 Oct 2017 T=72 °F
Ave Vel = 2460
Std Dev = 21
ES = 30
High = 2474
Low = 2444
N = 5
Very good group
140 gr Hornady Spire Point
43.0 grs AA4350 R-P new brass CCI-200 OAL 2.990"
18 Nov 2007 T = 75 °F
Ave Vel = 2428
Std Dev = 29
ES = 95
High = 2480
Low = 2385
N = 24
easy bolt life, nice rounded primers
140 gr Hornady SP greased
45.0 grs IMR 4831 wtd lot 2-22-2014 new R-P cases CCI 200 OAL 3.065"
2 Nov 2017 T=72 °F
Ave Vel = 2419
Std Dev = 19
ES = 43
High = 2439
Low = 2396
N = 5
140 gr Sierra Matchking greased
45.0 grs IMR 4831 wtd lot 2-22-2014 new R-P cases CCI 200 OAL 3.065"
2 Nov 2017 T=72 °F
Ave Vel = 2438
Std Dev = 12
ES = 30
High = 2448
Low = 2418
N = 5
140 gr Hornady SP (0.264") greased
47.0 grs IMR 4831 wtd lot 282 NNY cases Fed 210S OAL 3.050"
13 Oct 2017 T=72 °F
Ave Vel = 2633
Std Dev = 24
ES = 81
High = 2680
Low = 2599
N = 10
140 gr Hornady SP (0.264") greased
48.0 grs IMR 4831 wtd lot 282 NNY cases Fed 210S OAL 3.050"
13 Oct 2017 T=72 °F
Ave Vel = 2688
Std Dev = 16
ES = 44
High = 2705
Low = 2661
N = 10
Overmax load, primer cupping around firing pin, shiny rub marks on case heads
140 gr Hornady SP greased
45.0 grs H4831 wtd lot 01-06-2014 new R-P cases CCI 200 OAL 3.065"
2 Nov 2017 T=72 °F
Ave Vel = 2289
Std Dev = 9
ES = 16
High = 2296
Low = 2280
N = 5