I'll use "weak two" bids as a frame of reference.
My understanding of a "weak two" bid is that it is usually made with six cards of a suit, and at least five high card points (hcps). If that's all, they will be in the suit, that is KQxxxx or AJxxxx, and this would be done mainly at favorable vulnerability (not vulnerable vs. vulnerable). At equal vulnerability, you need either another honor in-suit (e.g. KQJxxx) or a side suit honor. At unfavorable vulnerability (vulnerable vs. not), you need both, for a maximum of about 10 hcps.
A "strong "pre-empt" at the three level would have the values for a "weak two" bid with a seventh card. The theory is that the extra "trump" would compensate (on offense) for the higher level, so you would go down as much as for a "weak two" bid.
A weak "pre-empt" would have the seventh card, but be about a queen lighter (and less likely to have the side value) than a weak two bid. It might range in strength from QTxxxxx to AQJxxxx with little or nothing outside. The theory is that the extra suit card compensates for a king "lighter," and your weaker defense (by one trick) means that you can "afford" to go down an additional trick on offense.
Are most expert pre-empters at least consistent within these two philosophies (or any other)? That is, do they pre-empt "narrowly" either with something like 5-10 hcps if using strong pre-empts, or 3-7 if "weak?" Or are there systems or experts that will run the whole gamut of say, 3-11 high card points for pre-empts?