Hard to say. In ProfileMaker Pro, you can use the MeasureTool to generate a custom target of virtually any size up to a limit (yesterday I output an RGB target for my 2400 that contained 11000 patches). I could have typed in 3600 if I wanted and had such a custom target generated.
There's most certainly a point of diminishing return here with patch size. For non linear printers like the Epson's using the native driver, I find using Bill Atkinson's 4096 patch target produces a tad better results than his 2700 patch target (which itself is a tiny bit better than his original 918 patch target).
The 11000 patches is for testing a new Spectrophotometer and I'll compare the profile quality with the 918 "standard" patch target to the Epson just for fun. The older 918 does a pretty darn good job.