This is a longish post, so please bear with me.
First, a bit about me. I've had my EOS 7D for about a year having well and truly out-grown various point and shoot cameras. I purchased this with the 18-200 3.5-5.6 IS kit lens as I was a little unsure as to exatcly which length lens I would require and this gave a great range when starting out. My main photographic subjects are horses (competing in various equestrian disciplines both indoors and out), motorsport and birds (both perched and in flight). I've noticed that 200mm is too short at times, particularly for birding.
During the first year I have also purchsed a nifty-fifty and been lucky enough to borrow a friends 70-200mm f2.8L a couple of times. I had my heart set on a new example of this lens (mark II) and started saving. I'm now in a position to part with my hard earned cash and buy some new glass however have been weighing up some options and would like to know your thoughts.
Purcahse Canon 70-200 2.8L IS II USM and a 1.4x or 2x teleconverter. There are a number of reasons I like this lens; mainly the speed for indoor events, but the weather sealing is nice piece of mind for dusty places and the odd rain shower. The teleconverters will provide that extra reach I currently wished I had when birding.
For the price of the above combination I can comfortably buy a Sigma 70-200mm F2.8 EX DG OS HSM AND a Sigma 150-500mm F5-6.3 APO DG OS HSM and still have enough change to buy a nice backpack to put it all in and perhaps a monopod or tripod.
So I'm a bit torn between the 2 options above and would love to hear your feedback and ideas. I'm not a professional so the L series lens might be "wasted" on me, however in most other facets of my life I'll buy the best quality I can afford, regardless if it seems excessive at the time. The Sigma scenario will provide a more versatile suite of lenses immediately and also give me the option to upgrade at a later date.
Looking forward to your replies.