bike vs mod production
At Boonville NY they have a big contest with 3 cuts in 20 inch white pine, cold start. A good 250 bike saw (not a Rotax, which is 325+cc) would probably do that race consistently in the 6 - 7 sec range with a top operator. I have personally never seen a modified production saw cut that race in under 10 seconds, but Matt Bush told me his Chauncey Varney 3120 on 1/2 alcohol, 1/2 gas cut it in the low 9s one year.
I'm not sure what saw Marcel used to run there in that class (when they had a production class) or what he ran for fuel, but he was always in the low 10s I believe. My homelite 750 was usually between 11.5 and 12.5 running pump gas and I usually came in second place to Marcel... One year they had 18 or 19 inch wood and I was in the 10s (though still 2nd place).
If you were looking for a direct conversion... I'm not sure there is one. In big wood you could probably say that the production saw would be 1/2 again longer than the 250 but in smaller wood I would think the difference would be a smaller percentage thanks to rpm vs torque.
Hope my rambling helped...
Mike