I think the best option is to buy your 28mm lens and an accessory finder (a cheaper CV finder is fine). Then two things happen. You can decide if you like the 28mm lens, and then decide if you like working with an accessory finder. If the first is a 'yes' you didn't need to buy a new camera, but if the second is 'no' you can expect to see an improvement in ergonomics with an M6. But don't get drawn into the idea that a .58 viewfinder is the way to go. It makes all the other frames look like a pea on a plate, and if you can see around the edges of the 28mm frame on a .72 camera this is a much better option. I bought a .58 M6TTL because I wear glasses, thinking it would be terrific. But the view with any other lens is so compromised that I went back to a .72, and because of my glasses back to quickly 'scanning' around the edges of the frame when using a 28mm. But if you only want one camera body to dedicate to a 28mm lens, then I admit the .58 finder could be the best.

Steve