Poncirus,

SO will produce full size vigorous trees. Nothing else was used for commercial planting over here until well into the '00s when tristezza was imported from Spain.. Planting in ground in zone 6 can only be done in a large heated glasshouse, I believe. In the pot they will quickly become pot bound, but citrus can be kept potbound. SO is the best rootstock for all common citrus, if you discount its susceptibility to tristezza apart from the Lemon on SO combination which is tolerant (or better Lemon on Orange on SO). But I suppose there's no tristezza issue in 6b.. SO is very easy to grow from seed with a large percentage of nucellar embryony.