Here is a list of pros and cons I found.... the thing is i doesn't mention any particular length for any particular bikes:
More swing-arm length has the following effects:
» The center of gravity moves forward, loading the front wheel.
» The turning radius is increased and turning is slower.
» Weight transfer forward on braking is reduced, the rear brake does more work.
» Weight transfer backward and traction on acceleration are reduced.
» The swing-arm arm is less rigid due to increased span length.
» Clearance to the inside of the rear fender and support loop is reduced.
» The brake torque link and chain guard must be extended, and links added to the chain. In
extreme cases a tensioner should be added to the lower chain row.
The shock absorber & spring presents its own problems:
If the extra swing-arm length is added rearward of the lower shock mount (usually the easist method, since it avoids re-locating the shock mounts):
» The spring and hydraulic valve rate becomes effectively weaker, because leverage against the
shock is increased.
» The shock’s travel (and therefore the maximum suspension travel) is slightly reduced.
» The rear wheel’s positions (droop, loaded, and full compression) are all slightly higher, the
chassis and seat are slightly lower, and a small amount of rake & trail are added to the steering.
» Due to the forward inclination the suspension becomes slightly “rising rate”, where the rate per
inch of travel increases as the compression limit is approached.