Thanks, that makes perfect sense. I guess my worries came from the fact that in my current company I don't know of any of the 100s permanent devs that came from a contracting background, so I sort of raised flags for me. That could possibly be because contractors dont often go back to permanent roles, rather than them being undesirable for a permanent position.
Really good point on the Math's side of the business. I am based in the UK, hence things like Health and Dental and very good and free, therefore no need for costly private insurance. Pensions, the same, although I would make arrangements myself to contribute to it privately also. Taxes and other deductions, I plan to hire a good accountant that can both ensure I have all my affairs in order as well as look after my financial interests. PTO/Instability is the only true financial downside I can see, however, for the latter (at least in UK) even if you are a contractor they need to give you 1-2weeks pay should they wish to terminate the contract early - which should keep me afloat while finding new work.
All that being said, I think the main difference between US and UK when it comes to permanent salaries is that the US has much higher base in average rates than when compared to the UK. Not to mention the buying power of that salary is order of magnitudes higher than over here. Therefore in a way, it seems more unlikely (if I were to be over there) to do contracting when balancing the pro's and con's of both options.
Thanks again for your words, and advice.