Big lenses are a serious investment, when you're shelling out £1000 and up you need to at least be able to get the best out of them.
I had the Bigma 50-500mm OS
I then got rid of it and bought the Canon 100-400mm f5.6 as I preferred the push/pull zoom action and the f5.6 was more usable than the f6.3 of the Bigma. I don't get too wrapped up in the differences of camera bodies as technology is so fast moving, buy one that does all you need it to, but always always buy the best lenses you can afford. Lenses for most people will stay with you as you change camera bodies over the years. Only when you switch to full frame would you need to change your EF-S or DX lenses.
On the subject of macro I have found it hard to use my SLR, and took most of my best macros on a set up which uses a Canon SX1 that i've mentioned before. There was just something about this camera that I just bonded with and it was a perfect tool for stalking insects etc.
When I visit RSPB sites i'll generally spend all day hunting and stalking the creepy crawlies. This is one of my favourite macros of a Hoverfly in flight:
While it's not technically brilliant and has some image noise it's still a hard thing to capture. The beauty of the SX1 is that even at these extremes is that it can shoot 10mp RAW files at 4fps, which is a rarity for bridge cameras.