Great decision for Murray to start playing around with specs. He needs something that helps him finish points more offensively to compensate for his slower movement. He should change his swingweight along with extending the length.
The setup that worked for him in 2016 won't work now.
I once spoke to Roman P. about the topic of changing racquets and specs to fit the times.
He mentioned that he had been trying to get Berdych to switch to a lighter frame for the last few years of his career (used 360sw, ~370g) and what he was using was too comfortable for him, he was unwilling...
I hate to bring back the concept of SW1 and SW2 from @travlerajm ;) but that is essentially what we have going on here.
SW1 would be the range of light swingweights from 300s-320s.
Holger Rune - 315
Liam Broady - 315
Yoshihito Nishioka - 315
Adrian Mannarino - 325
Nick Kyrgios - 325...
Holger Rune, up and coming player ranked around 500 also uses 314sw strung.
All a lower swingweight means is you have to compensate for the loss in power with RHS. It does not inherently mean it is more or less suitable to the pro game.