The Slimline (4in circumference) is super easy for me now, and before I stopped using it, I was getting relatively comfortable with the Red Boy (5.25in circumference) - I could get it in in 2 minutes without warmup. I'm still getting used to the Butt Tingler's 5.5in circumference, but it's not too much trouble after a little coaxing back and forth with plenty of lube.
ANYWAYS, all that to say that I've already purchased the njoy Pure Plug Large Stainless Steel Butt Plug http://www.lovehoney.com/product.cfm?p=9042, which, with its 4.7in circumference, I'm pretty sure I'll be able to handle no problem once it arrives on Tuesday. My question is this: is it worth purchasing the njoy 2.0, which boasts the hefty 5.6in circumference, and will I be able to handle it at this stage? How does inserting the metal compare to the silicone? Insertion/removal are my main areas of concern at the moment.
I would wait and see how you get on with the large first. Whilst the measurements sound comfortable/manageable for you, you need to take into account that metal is much heavier than silicone.
I usually find glass and metal toys feel larger than they are too, as the material has no give. Silicone toys generally have some flex or squish to them, which is why they're easier to insert and get used to. There's no rush to progress to the largest toys straight away, pace yourself a bit and don't rush or you may end up hurting yourself!