Willem
You are following a very very similar thought pattern to myself. Based on your post I'd say you are where I was about one year ago. This is what I have concluded/learnt in the year since then
1. You just don't know what returns are possible. You can read lots about it, ask here in the forum, you can speculate, but until you actually develop a strategy and start implementing it, you just won't know what is possible, and no amount of speculation will change that
2. It's true that the "big boys" don't make much more than 10%. Heck, 2% above S&P500 consistently year after year is considered very good, if not amazing, performance from a hedge fund. The key being _consistent_
3. There is something you are not taking into account. Trading millions or billions is an entirely different game to trading a few thousand dollars/pounds/euros. When trading such large sizes, there are many opportunities that simply aren't there
4. I even thought about the moving to a lower cost location, which is still very much on the plate, but I'll consider if I ever decide to leave my job and trade full time. Sunny Spain sounds appealing
I know it's possible to make money consistently in the market. In a firm I used to work (major IB), there was a guy doing algorithmic trading in German bond markets, and was making consistent money. Not earth shattering, but consistent.
You sound just like myself. Analitical, likes to weigh all options, very risk averse, dislikes gambling. All strengths based on everything I've seen/read so far.
By all means, keep researching, but you won't get a straight answer. Your only options will be either to give up, or to go ahead and invest the time to develop a strategy.
As for myself, I've decided to answer this question once and for all. I'm currently starting to develop a business plan (this is a business venture after all) which will require some time investment initially (to develop the methodology/strategy), and assuming all goes well, some money investment to try out the strategy(ies). If it all works, great, I'll consider it as a full time career. If it doesn't, I'll have invested the time in getting the answer(s) I was after, close this chapter, and move on.
It'll probably take me a couple of years to answer my questions, but at least I won't left wondering "what if" for the rest of my life
I hope that helps, and best of luck!