First of all, which Crowley and Tripp are you thinking about?
There's a ton of information on ribbons and rock guitars on the board, a simple search would give you lots of help.
You could start with these:
Ribbon for heavies. Dissatisfied with dynamic mics on distorted guitars! Best Ribbon for Rock Guitar?
Myself I use the 121 for close cab miking and the AEA for room, so my advice is to get both of those
