10AWG wires are not going to be easy to solder, especially not with a cheap soldering iron. This would probably be more appropriate for like an automotive style soldering gun (which, in general, I HATE to use - but then again I haven't used them often so I could just suck with them).
What's the application? Will this be wire-to-wire? Is crimping an option?
Even a cheap 80 watter will probably not be able to do this job (and if it does it, it won't be easy). If you do buy one of those pencil irons, make sure to NEVER use it for anything precise, and I REALLY recommend a stand. These things can be a real fire hazard, especially the high-wattage ones.
If you do use it, load that sucker up with solder. The more you use, the easier the heat will transfer, but obviously at the cost of a potentially sloppier joint. Make sure not to make a cold soldering joint.
Honestly, I wouldn't use a soldering iron lower in quality than my ~$75-100 Weller WES51. I recently got a JBC iron after watching Dave's review on his, and compared to that, my WES51 might as well have cost $20. The JBC is just so much faster at everything. I can't imagine using an iron lower in quality/thermal capacity than the WES51, especially to solder relatively large-gauge wire.