Well the Portamig is well known for going very low in power so its ideal for car work I should imagine, I use mine on ornamental steel up 10mm square bar and it does the job no problem, never had to use full power yet.
I dont have any experience of the lincoln but I would have no hesitation in recommending the portamig.I own a 211 and do a similar range of thickness's to yourself,it never struggles and does the job really well.Best money iv spent on tools I reckon.