I own a CZ 550 FS in 6.5 x 55, reload for it and hunt with it a bunch. Have killed a pile of deer with it out to 300 yds. I have no problem stabilizing 140 gr bullets. I normally load 140 gr Hornady SST's which group around 1" (3 shots) at around 2750 fps. I normally get an exit hole on broadside shots.
I do not think you will have any problem with 140 gr bullets in your rifle. In fact, I think that is the best balanced bullet for this caliber.
What he said.
Firstly the CZ550 6.5mm has a 1:9 twist.
Secondly is shoots a 140gr Sierra Game King with serious authority. For me 0.6MOA.
Thirdly is shoots a 120gr Sierra Pro Hunter and a 130gr. Nosler Accubond with equal authority. Also 0.6MOA, in fact it is my most bullet weight friendly rifle. Have not tried heavier as I use calibre changes rather than bullet weight changes.
My go to bullet is the 130gr Accubond, greatly reduced meat damage and you generally will have an exit wound.
I cannot offer any load data as we run local powders here, a Somchem S365. But some advice would be to seat the 130gr. Accubond 0.025" off the lands, to run a normal Large Rifle primer with probably IMR4350 which by all counts is almost identical to our S365. I was running at 2 850fps.
I believe that the CZ 6.5mm does not have as long a leade as some would purport as I can get a 130gr Accubond into the lands if I wanted.
I think you would do equally well with a 130gr. Partition.
Finally, when I got my 6.5mm out of the box it could not shoot. I soon established that the recess for the recoil lug had not been cut deep enough and that this caused the action to rock about the recoil lug. Check yours as a matter of course.
I always bed and free float and would recommend you do the same, the barrel is already floated so all you need to do is to bed. The CZ action was also a bit rough, ask you gunshop for a burnishing compound and work that bolt 500 to 1000 times before you go shoot, slick her up and you are good to go.
Wonderful rifle, wonderful calibre, wonderfully accurate, you will not be dissappointed.