I'd echo most of the above comments...
Basically, with you really only having 4 total units in your army - two of which are big infantry blocks, and another being your steg - you're going to get run around by any army that has a good amount of skirmish/cavalry type units. The champions don't bring much for their point cost, and even the banners might be a bit much at this point level as your ability to cut down those attacking you should hopefully balance out the CR.
Also, you'd have to hope for ideal terrain placement - as warmachines and gun/bow lines will cut down your saurus long before they can get into combat (even with the help of the steg's ward save against shooting... attrition will wear you down). To cross the table quickly to deal with either of these, you'd want either the above mentioned terradons, or a group of chameleon skinks.