The upgrades should actually be the same, at least per the T&C, as both should get a 'preferred room'. However on rare occasions a hotel might be more likely to upgrade beyond the T&C for a Gold. YMMV.

Best way to think of Corporate Preferred or Preferred Plus (the latter you get just for having the SPG Amex or being a AAA member IIRC) is that it's Gold without the 50% bonus points for eligible hotel spend.