I orginally posted this in the 'new guy' section and it was suggested that I would get a better responce in this section.
i'll offer some info... first off, the "sweet spot" you refer to is sweet for chain adjustment only. it's not really all that sweet as any adjustment alters ride height and wheelbase, albeit, not by much. i think the reason it is at the 4-5 o'clock is it offers a compromise between altering those two other measurements. in addition, i could imagine in any other position, the torque laid down by these bikes could cause the eccentric to rotate...particularly if the pinch bolts haven't been properly/sufficiently torqued. the real sweet spot lies in the swingarm angle. so, if you had taken measurements of the ride height, then spun the eccentric towards the 3 o'clock to remove excess chain slack, you would definitely have to adjust the ride height and account for the extra length in wheelbase. turning the eccentric to the 3 o'clock could give you the necessary room to run the taller tire, but the geometry is now very off. the stock ride height adjustment rod may not provide enough purchase on the threads of the rod after you lock it down with this extension that brings your ride height back in line. you'll need to watch that your hugger, if so equipped, doesn't get eaten up, too. - aftermarket ride height adjustment rods are available. the most important thing to consider when adjusting ride height is "the window". while you may be able to move the swingarm up and down about 2" at the axle with the adjusting rod, the window of what "works" is only 5mm wide. get outside that window and all manner of handling ills will present themselves. they will seem to originate from the front end but no amount of adjusting the front will cure it. get the rear in the window and you can do whatever you want up front. - there is an aftermarket tool specifically made for measuring the ride height. it mimics the unavailable ducati tool. on the 748/996 chassis, this window was 137-142mm. with the newer chassis' longer swingarm, that measurement could be slightly taller, or near the same. how? they went to a bigger axle diameter and the "ducati" way to measure was from the edge of the axle...not its center. unfortunately, i don't know what the measurement is for the 848/1098/1198 nor have i found it online. also consider that the taller tire has to be taken into account when you make your ride height adjustment. half the difference in height between the old and new tire is the measurement you will be concerned about but you'll have to consider what needs to be done up front to bring the bike's total geometry near to where it was. fwiw, i think your gear change is too much. going up two in the rear with the stock front is quite sufficient for most track work. unless you're doing daytona or some other highspeed drafting track, gear the bike to pull redline in 6th. this might be any combination of stock/-1 up front and stock/+x in the rear. whip out your calculator and make a list of the various ratios so you'll know what's what. having two chains for your optional gearing changes could help.
