You know, Chris, buying an AV receiver is very like making love to a beautiful woman...
First you choose the one that looks the prettiest, and you take it home, and for a while everything seems lovely. Then you wonder whether you might be having more fun with the one that looks plain, but seems to have more to offer. Finally, someone tells you there's an even better one due any day now, and you wonder whether you should have waited before doing the whole chocolates and flowers thing and rushing into it.
I'd wait and see how good the new Onkyo 606 is before taking the plunge. It looks like it should be at least as good as the TX-SR605, and with more on offer - sorry, better facilities - and if it's not, chances are you'll be able to get a good price on the 605 when the new one is out.