Regarding the earlier Stealth do you mean the Pre F16 rig model (Stealth 'R') or earlier? The pre F16 rigs had a lower centre of effort on the rig and may have been less sensitive to trim and 'easier' to sail. With the lower C/E less righting moment would be required.
It is worth remembering no two boats are identical with often considerable differences in weight and stiffness of many components. Add variable crew weights and wind strengths and it becomes difficult to make valid comparisons.
As Smiths cat mentioned his Dart 18 was faster than his Javelin. In the right hands the Dart can be blisteringly quick but not on all points of sail. The more tunable race oriented boats often make better vmg around most of the course.
Another thing to consider is the different sailing styles of the crews. Some people sail quite 'aggressively' with constant trim and course adjustments potentially leading to poor sail trim and more rudder breaking, others feel the boats power and let the boat sail where it feels fastest, and then we all make our own judgements around the course. The trick is take time to learn your boat. It is the knowledge and skill of each individual to understand and use the strengths and weaknesses of their own craft that will lead to success. Follow others if you want to learn, but be prepared to learn that another boat/setup/style is not necessarily better for you.

Cheshirecatman