Buy another steel bike or get aluminum?

I have a crmo geared Surly Cross check as my main commuting workhorse bike. I have a cheap hi ten fixie that I want to replace/upgrade. I have been thinking about getting a Kilo or something similar with a better light weight crmo frame but recently I have been thinking about getting aluminum to mix it up such as SST from BD or maybe build up a Leader or something similar. This would be more for fun rides and training rides with some of my road/tri buddies for a work out. Probably will never see the track regularly.