The 420 also has a lot more features, the presser foot pressure adjustment, automatic thread cutter, the needle threader is also more advanced than the cs6000i. It has a lot of the features that were on my babylock espire for a 1/4 of the price. You will love those features and wonder how you lived without them. I'd still consider the cs6000i as a side/class machine because it is a great little machine and as I said the pc420 is mostly metal frame so it will be a great deal heavier than you lx model. going computerized from your mechanical will be a step up but I do think you can grow more with the pc-420. or you can always get the cs6000i and get a straight stitch PQ1500s,they run about 500 and that has a 9 inch harp more than enough for FMQ, not sure on the harp size of the 420