Never sailed a I20, but have seen a few around when sailing my Hurricane 5.9 (another 20 footer), And my opinion of the Inter 20 was a very solid boat which looked like it should go fairly quickly, but never really got there in the UK; probably because the Hurricne 5.9 was a well established boat already, sailed by good sailors that could usually beat the I20 over the water and the Hurricane (at the time) was only 2 sails.

If the inter 20 had "made it" in the UK before the Hurricane 5.9, it might have been a different story; have to agree with Wouters comments on the bow shape of the I20, but this did mean it was very difficult to pitchpole.