Barrichello was usually ahead of Irvine in 1994 and comfortably outscored him.
In 1995, Irvine was much stronger relative to Barrichello, especially in the first half of the season. Barrichello had some problems with his braking technique which took until the second half of the season to solve, so Irvine was usually the faster Jordan driver up to this point, but they were more evenly matched thereafter. The cars were very unreliable during this season, however, so their final points totals (Barrichello 11, Irvine 10) are not particularly helpful in assessing their relative performances, as both lost several good finishes due to car failures. I think that at the time, the general impression was that Irvine had the more impressive season overall (e.g. Autocourse put him ninth in the Top Ten, with Barrichello not featuring), ad that his speed had out-psyched the previously ascendant Barrichello, whose career subsequently stalled in the midfield for several seasons until he was signed by Ferrari for 2000.
Irvine's Ferrari record is of course inferior to Barrichello's, but in my opinion this is almost entirely down to the fact that the cars he drove - the F310, F310B, F300 and F399 - whilst competitive, were not in the same class as the F1-2000, F2001, F2002, F2003-GA, F2004 and F2005, most of which were the pacesetters of their respective seasons. I think that Barrichello would also have struggled to produce consistent results as Schumacher's team-mate in the late 1990s, and that Irvine would have been a far more dependable number two driver had he been with the team in the early 2000s. Overall, however, I would rate Barrichello slightly above Irvine due to the longevity and consistency of his career, and I also got the impression that he was a little faster than Irvine in 1995 when he was happy with the car.