This took 46.5 seconds on 1140 files. Estimated time to rename 7500 files would be ~5 minutes. This is on a 2.16 Ghz Intel Core2Duo.

Code:
proc rename {file} {
	if { [file isdirectory $file] } {
		foreach nextFile [glob -nocomplain "$file/*"] {
			rename $nextFile
		}
	}
	file rename -force -- $file this_is_a_hack
	file rename -force -- this_is_a_hack "[file dirname $file]/[string toupper [file tail $file]]"
	return
}


On Windows, download ActiveState Tcl if you don't already have it and paste the rename procedure in tclsh.exe. Then do:
Code:
rename name_of_parent_folder


The "this_is_a_hack" portion of the code is because of a silly bug in Tcl that doesn't let you rename a file to itself with different capitalization on Windows. It makes it take twice as long, but it still beats 45 minutes.