Reddit mentions of PANASONIC LUMIX G LEICA DG NOCTICRON LENS, 42.5MM, F1.2 ASPH., PROFESSIONAL MIRRORLESS MICRO FOUR THIRDS, POWER OPTICAL I.S., H-NS043 (USA BLACK)

You'll be going from ~1.6x to ~2.2x (assuming you're filming in 4K). If you're using a 50mm lens on your 550D, you're getting ~80mm field of view equivalent. If you want that same field of view, you'll need to get a ~36mm lens for the G85.

Something a bit longer and will still give you a pretty shallow depth of field is the Panasonic 42.5mm f1.2 ASPH, but it doesn't come cheap.

IMHO Oly's 45mm is the best native lens at that focal length and price range. [Panasonic's 42.5mm f/1.2](http://amzn.to/1r4Oqxc "Panasonic 42.5mm f/1.2") is a stop faster for better low-light and shallower DOF, but at over 4x the price of the Oly, it's more of a rental lens than a purchase for me.

Well, with this endless budget of yours. I'm going to go all out if you don't mind.

• Wide Angle: Pana Leica 8-18 f/2.8-4 or if you want smaller the Laowa 7.5mm f/2
  
• All round zoom lenses: Olympus Pro 12-40mm f/2.8 and the Olympus pro 40-150mm f/2.8 with a 1.4x converter if you want
  
• Primes 1: Olympus 75mm f/1.8 and 45mm f/1.8 and then sell the 45mm to make a profit
  
• Prime 2: Panasonic Leica 42.5mm f/1.2
  
• Prime 3: Sigma 30mm f/1.4
  
• Prime 4: Olympus 17mm f/1.8

If I could afford it i'd replace my 12-35 and my 25mmf1.4 with the 10-25!

If I was buying the 10-25 like you I'd get the 35-100 f2.8 which is on offer right now on amazon, referral links included.

I'm also a big fan of my 42.5mm f1.7 for portraits and bokeh time. You could get the 42.5mm f1.2 , but it's manual focus only more expensive. Amazing quality piece of glass though. I love the 42.5mm focal length, I suggest you check it out :)