New IS Zoom? / DO question

Apologise if this has been covered before, but I have a lens quandry.
I have recently got a 350D and a 17-85IS lens (very happy with them so far!). I am currently borrowing a 75-300 USM (maybe III - can't remember! edit - no, it's a II) from my father (spare), which is OK.
I am looking to get an IS tele-zoom. I originally had in mind the 75-300IS, but have since read mediocre reviews of it (first gen IS etc.) so have tended to lean away from it. I liked the idea of the 70-300DO (it's size would suit my usage), but it has mixed reviews and is quite pricey (about 2.6x that of the 75-300IS).
I suppose my question is does anyone think/know if canon are likely to replace the 75-300IS with a newer model anytime soon? I have a trip to MAKS airshow, Moscow in Aug and the NAS Oceana show in Sept, and am looking to get my own lens for them (I can live with the 'loaner' 'til then!).
If no new lens is on the horizon, is the DO worth the extra (I know its a bit of a subjective question, but hey!)
Cheers!

Dew,

welcome to the forum!

Check out this article, it gives an example by comparing shots of the Canon 75-300 IS, the Canon 70-200/2.8L and the Canon 70-300 DO.

The 75-300 IS will basically give the same image quality as the Non-IS lens you're using at the moment.

Best regards,
Andy

Andy,

I had seen the article, but thanks for pointing it out - I hadn't noticed the link to another page of examples. It's a tricky call whether to foot the extra for the DO (difference between £290 & £770!). I'm not keen on the first gen IS with no panning mode, but I'm sure the IS will help as I won't be carrying a tripod, and trying to catch aerobatics doesn't exactly lend itself to their use!

I'm just gonna sit tight for now and maybe see if they release a newer 75-300 (after all, its what, 4 years old or so now), and hope the DO price falls before August!

Cheers
Chris