The original Spectral Archer classpath was designed specifically for Frogarth with the 3e rules and balanced his spell caster level against his Intelligence. His caster level never progressed faster than his ability to cast higher level spells. His low starting Int meant that this was slow at best, such that Wiz3 was at level 8 (Int 12), and Wiz5 at level 12 (Int13). After that, I went with straight Fighter levels for the BAB.
With the release of the 3.5e rules, including the Eldritch Knight prestige class, I have revised the Spectral Archer classpath to take advantage of it.
I also threw out the artificial constraint of Frogarth's Int, as any character, especially smarter ones, might want to take this classpath. Frogarth can use magic devices like a headband of intellect to increase the level of spell he can prepare, or he can just use higher level slots to prepare lower level spells and just go off and pout at the "inefficiency" of it.
Original Class Progression from level 1 to 20: Rogue, Fighter, Fighter, Rogue, Diviner, Diviner, Rogue, Diviner, Fighter, Fighter, Diviner, Fighter, Rogue, Fighter, Fighter, Fighter,
Fighter, Fighter, Fighter, Rogue