I was thinking about your original question, and to be honest for the amount you want to spend i think I would hold off till you can save a little more, then purchase a welder that will do what you need it to do.
I have both Miller and Lincoln welders and love them both. At the time I purchased my gas welder, I thought Miller Bobcat with the bigger engine(Kohler) was the best available. I bought that and the Plasma cutter for it at the same time both new and both at the same dealer. While I still like Miller, and for many things they are the best... ... I love my Lincoln welders. I like you started with a Lincoln Weld PAC 125. I bought it when I first started my company, and I paid for it the first week I had it. I form the start only used it with non-shielded wire and a tri-mix for gas. That welder lasted for about 2-3 years, and I quickly out-grew it. i sold it to a buddy and he is still using it to this day. The welder I replaced it with was a Lincoln Sp-250 (255) and I have love it since I purchased it. This welder is everything I think a welder (MIG) should be, it works every time I need it and does a great job with absolutely no,NO problems. I weld 1/4" material all the time and it will do a great job bonding the two metals in one pass, same with 3/8" stuff. Of-coarse it depends one what the material is for, normal run of the mill stuff and one pass is fine, others will require more . The Lincoln SP-250 is an ideal MIG welder, it comes standard with a 12. 5' gun, and in 95% of all situations, especially in the shop thats plenty. The normal consumables are not very expensive and to this date I have had zero problems. No feed issues, nothing. Of-coarse a good maintenance plan is also good assurance that everything will go as planed. I just recently purchased another Lincoln welder, this time it was their Precession TIG 275 W/ undercarriage and water cooler. I have just started with this machine but have no doubt it will continue in the prime Lincoln tradition. I looked around and even used both Miller and Lincoln TIG units before I bought my Lincoln, they have in my opinion the best units. While I like both Miller and Lincoln, I think you would be best if you also stayed with either brand. They have both been around for ever and both are used everyday by welding professionals in every country around the world. Good luck on your new welder purchase.