I'm not a expert by any means no way no how.
The 5105 with the 5100 muffler otherwise stock would eat a heavy stock MS290 lunch supper and breakfast next day.
Now I have never ran one with the epa 5105 muffler on it.
Never ran a 310, only 290 and 390. To me if someone is going to carry the weight of the pig they mise well get the 390 65cc. Then again there like you say I would go 6401 or it's replacement for same money and little more weight.
I still like the 7900 OEM top ends better. I have ran the BB7900 stock on 2 different saws and the OEM is just better to me. 7900 OEM ported wins IMO too. Now this is JMO.
The 5105 with the 5100 muffler otherwise stock would eat a heavy stock MS290 lunch supper and breakfast next day.
Now I have never ran one with the epa 5105 muffler on it.
Never ran a 310, only 290 and 390. To me if someone is going to carry the weight of the pig they mise well get the 390 65cc. Then again there like you say I would go 6401 or it's replacement for same money and little more weight.
I still like the 7900 OEM top ends better. I have ran the BB7900 stock on 2 different saws and the OEM is just better to me. 7900 OEM ported wins IMO too. Now this is JMO.