Can't say anything for the 540s but I've used 520s, 580s, & 510s and they're all great lights.
The 510s are 4" and 520s are 6", I assume the only real difference is the 540s being 5". I can't remember what bulbs come in the 540s but it's definitely worth upgrading to PIAA xtreme white 85=135W bulbs if they only come with 55Ws.