I generally feel that you buy when you're ready to buy based on your current situation. If your current computer isn't up to snuff, just buy. There will always be another around the corner that'll be better than the one you buy today. That advice is as old as the hills, I realize.
I also generally advise getting the very best you can possibly afford, but as I get older and my priorities change (and as the tasks I do get more distributed among several devices), I find myself adhering to that less and less.
I also generally advise getting the very best you can possibly afford, but as I get older and my priorities change (and as the tasks I do get more distributed among several devices), I find myself adhering to that less and less.