There is actually not a lot of variation in the Omega lines, particularly with regard to the barrel/actions. Blued, stainless or Weathershield (avoid the Weathershield imo). Standard 28" barrel or shortened (X7 or Dream Season, both fluted and the X7 being the shorter of the two). That's about it. Some older barrels had a faster twist, and there are a few .45 cals out there. But my guess is +90% of the barrels out there are 28" .50 cal.
Stock options - laminated (regular or thumbhole) or synthetic (regular or thumbhole). The X7 only came in laminated, the Dream Season only in synthetic with "FlexTech stock with energy burners to reduce felt recoil" (a gimmick imo). Boyds now makes laminated stocks which I hear are pretty decent. The X7 and Dream Season barrels can only fit the stocks made for them.
The most significant thing I would look for in getting a used Omega is to look for a barreled action that has welded lugs which you will find in older Omegas. When the Z5 was introduced it was a "budget" Omega. To save money, T/C opted for lugs that used hex screws to attach them to the barrel. Soon, they started to use the hex screw on all their Omegas, including the X7 and Dream Season. In short, they suck. They get loose and cause accuracy issues. On my X7 it has been a constant battle to keep them tight. I finally started to use Loctite RED (263) and the screws seem to be staying tight. So if you can inspect before you buy, take off the stock and check the lugs. Welded are better.
