Bullet weight in and of itself has no relationship to accuracy. Question is, do you NEED superglides? If the regular sabots load ok then you will get WORSE accuracy with superglides -- a tight sabot is good as long as you can get it down.
Some guns seem to like a certain velocity range. For example, max accuracy with the 200 Shockwave in my Omega is 110gr (2050 fps). Since the gun is rated to 135gr loose 777 I'm not using all the power I could, but accuracy is #1. So this year I moved up to the 325gr FTX and have also tried the 300gr Shockwave, both of which go 1950fps with 135gr loose 777. So I get near the same velocity as a bullet only 2/3 as heavy and use the capacity of the gun's power.
The Dead Centers are another story. Somewhere between 1800 and 2000 fps your accuracy will go to crap because the soft lead bullets can't handle more than that before deforming (their BCs are WAY inflated anyways).
There are a number of other reasons your groups won't shrink. The barrel could need floating, the action bedding, etc.