See, that's where I'd disagree with the prevailing mindset that "more grain" = "better." All things being equal, that equation is going to be true, but all things aren't equal, especially if you've got constraints on your system.
The question really shouldn't be, "How much grain can I cram into my system?" It should be, "What amount of grain gives me the best final product (and/or is the most fun to do)?"
If you're someone who likes pushing the envelope (a description that I'd guess probably applies to about 90% of HBers) or are making a steady evolution to going AG, then by all means, use as much as you can fit. Otherwise, figure out what ratio makes your best beer and go from there.