Wildbill - thanks I know. But I couldn't resist. Don't get me wrong it's a wonderful, useful lens, just that it's as much of a pain as everyone warned me.
Thanks for the responses everyone. Regarding spacing, for me at least, there is a significant difference between 72 and 90 so I've never felt like those were too close. But it could be if I had a 110 I'd find it wide enough and not use the 90 much. Not sure. Perhaps I'll try to find a rental 110 and see. Regarding the spacing between 110 and 150, that's not too close for me either (used to have a 120 and I found much use for both the 120 and 150). In landscapes I used 120, 150, 300. Interestingly I've never needed anything between 150 and 300.
The kit as it currently stands is 72, 90, 150, 300 (in the old days as I mentioned I also had a 120 in there). If I got a 110XL I guess I'd either add it to this kit or replace the 90 with it. Or I can leave it as-is and try to get a slightly less bulky 90, like the Rodenstock perhaps.
mrsmiggins: The 90 XL can be quite useful on 4x5 for architectural work, although I agree the 110 image circle is definitely overkill for that format.