Try combining a distortion and an overdrive pedal, if you tinker around with them you can get that grail tone where the distortion is just about to spill over to feedback (sounds great for lead work). I've heard Petrucci use a similar tone but then again he plays through two super freezer sized racks of gear;-) Best stomp box/floor pedal I got was the Line6 DM4, its got everything from Hendrix to Yngwie to Metallica and beyond. All the major pedals combined in one, check it out!