I fear you're missing out the wrong Max versions Alan. :): Max 8 was a great update for games and 2008 (which I've just moved us to) has proved very solid too. Way faster for large scenes which is great. 9 and 2009 are both rendering releases so not of much interest to game folk. Good luck with Blender.
I'd be keen to hear from people experienced in modeling in Max that have moved to XSI. Every time I've tried it I've found that despite having lots of cool features (like ICE), the basics are just not there. As with Maya I have a hard time doing any architectural or environment modeling in it.
For instance- There's no real world scaling, there are loads of apparently needless hotkeys (about twelve just for selecting wheras I have exactly none in Max, I just stay in Move mode), not all selection modes work the same way (some select through, some not, you can't stay in move mode, you have to constantly go back to select to fire off modeling tools, the snaps are very basic, you end up having to move the pivot every second move. The uv tools don't seem to have much for mapping landscapes (although I do use a few scripts in max for that stuff). I haven't found any automapping or unfolding tools at all.
But then I'm very green to it. I'd like to hear from people that have made the move that are finding it faster. I appreciate that both XSI and Maya are great for animation, but we don't really do that at our place. Any animation is done externally. It seems to me that there isn't really anything like Max for environment modeling and mapping. There's definitely room for improvement there, but everything else seems designed for characters.