I've only ever capped Zihark's HP twice. He starts way too low; I mean, by the time I would get Edward to a level 5 swordmaster, he's probably have 37, where Zihark only has 30.
Otherwise, Zihark is just good because he caps like everything.
Mia has boobs; nuff said.
Pelleas can be really good if trained and BEXP'd a bit. I only use Illyana cuz she's actually the only one who can use Rexbolt. Soren is just awesome, and Rhys..
I dunno why I use him. Mickey can do all light magic stuff and staves.
I use Reyson cuz I capped everything for him with BEXP and transfer data.
I used to use Gatrie, until I realized Nephenee's just cooler. But really, Aran is the better choice, because Radiant Dawn is sexist.
I never use mounted units anymore. And really, I love using Sothe; it's too bad he's totally outclassed by Volke though.
Good luck with the speed run!
EDIT:
Give Reyson the boots, too. And Celerity if you can. Then it's just ridiculous.