Appreciate some advice folks. I'd like a telephoto, the 100-400GM has my attention... I'm sure it's almost "bag of primes" good but I have a 1st gen Sony A7, and a Samyang 35. Basically, not too heavily invested into the system, not blazing AF like the latest gen and £2500 shows a lot of options, not just Sony lenses - and even, looking secondhand, maybe even MFT/SLR - even APS-C - combining a body and lens (and keep the A7/35 as a discrete separate combo).
I like and have tried the 70-300G (£1000), tried the 100-400GM (yes, better, IMO not £1500 better but still great)....But for someone like me, £2500 could mean...
Used MFT body and Pana 100-400 - or even 200/2.8. Oly 300/4 out of budget...
Sony A6400 or A6300 and 70-300G....
Sigma 100-400 (or even 150-600) on MC-11...
Canon or Nikon APS-C DLR and used anything tele within budget...
Fast AF, decent quality at ISO 1600 in U.K. light, croppable feather detail not mush, and reach. Hmmm. We British togs know the good light seen in USA reviews doesn't translate here. What would you do to spend my £2500?