Tejada over Giles. Position boost is very very important.
You can find plenty of outfielders who will hit 25-30 homers and drive in 100 runs on the wire. Jay Gibbons could do it, Reggie Sanders hit 31 homers last year. Just off the top of my head. There are plenty of guys like that who likely are not on anybody's teams. You have to look at it from an entire team perspective. Even if your projections are accurate, you need to figure out what your projections would be with your SS/OF combo before and after this trade.
If you have Tejada and trade him, who would you replace him with? Would that guys production plus B-Giles be better than Tejada + your current outfielder. If you have Giles, would Giles + your current shortstop outproduce Tejada + replacement OF? I don't know what you've got in the works, but I'm willing to bet your team is better off with Tejada on it.
Rest in peace Mitch Hedberg. I name my fantasy team "Buoyancy of Citrus", in your honor.