I'd like to point something out regarding the rather martial image of your character. In terms of raw combat abilities, a 20th level wizard has a slight edge over a 10th level warrior. While the wizard can't use superior weapons and armor, a PC wizard will have many times more magical items, enough to give the wizard a substancial edge. While you won't be beating up big dragons without a specific build and Tenser's, a 20th level wizard that doesn't completely ignore physical attributes can beat up normal guards, vets, and probably even some elite guards without resorting to spellcasting. All you'd need is a single fighter level or martial weapon proficiency so you have to use a lame weapon.
In terms of raw power, the wizard is pretty damn good. Powerful spells, and great flexiblity. However, if you go Epic, there are some complications. Relative to character wealth, SR items become cheaper and cheaper, allowing both other characters and villains increasing levels of SR. Even stuff like Epic Spell Penetration stops cutting it. Also, the monsters have Super SR too. Pseodonaturals are especially bad because they have SR equal to 5 times HD - a tiny increase in monster power can result in a huge change in your ability to land spells. Other people have complained about saving throw DCs as well.
Between True Strike and taking Penetrate DR at level 21, a melee character can ease through the pains of growing into epic levels. However, there's no such work around for a character relying on direct spells. I hope you like to buff others, or summon stuff. But summoning sutff isn't bad at all, and custom Epic summons might be a cool way to go.
While the Spellsword isn't as great as a Persistent spell using cleric, it's still pretty dang good. I can put up a 15th level spellsword based character if someone wants to see it. While it's not exactly a smackdown, I think it's both effective in combat and fairly versatile.