It's subjective in some respects...
Without a doubt.
I looked at a GI 275 in ADI mode only. After looking at a couple of videos on YouTube I found it interesting to note that the display "appears" to be bigger than what I saw in person.
One of the things that I think makes the GI 275 look smaller in some cases is the adapter plate that is used to fit it where a KI-256 (AI) or KI-525 (HSI) used to be:
This is ours, and I think is a good comparison with the KI-525 still in place. Our KI-256 attitude indicator had a similar bezel arrangement, and so while the instrument itself is smaller, the presentation is slightly larger.
I get what you're saying about the "crunched" AI when the tapes are in place, but you don't have to have the full PFD setup - The AI can display in three modes: Basic (with no tapes), 3-in-1 with airspeed and altitude tapes, and 4-in-1 with the track/heading tape at the bottom:
I think the argument could be made that the HSI presentation is actually larger than the G5 HSI, although ironically to my eyes it still "feels" smaller.
Looks like there's no argument, it is definitely larger:
I know what you're saying, though, and certainly having the corners available for additional information is nice. I'm still going back and forth about whether I like the touchscreen or not. I'm not a big fan of the menu structure on the G5 that's necessary to do almost anything, but I'm also not sure I like touching the screen to select something to change either!
If it was possible to pair up a G5 ADI and a GI 275 HSI I'd consider that, but it's not, so until I can add a GI 275 ADI as my "backup" ADI to drive my autopilot, it'll just be G5s for me.
Yeah, it's too bad you can't mix and match. We might have sprung for the HSI right away if it could have been a G5, but I understand why Garmin doesn't make them work with each other. It'd make BOTH units more expensive, and we'd likely have needed to spend just as much to do that (if it were possible) as we would have in reality with just getting a pair of GI 275s anyway.
Really, it's hard to go wrong either way. If it weren't for a working autopilot that we've already put a ton of money into (before the GFC 500 came out), we'd have gone with the G5s when they first became available. The GI 275 will allow us to keep the autopilot going for the foreseeable future while allowing us to ditch the vacuum system, and should we replace the autopilot it'll drive the GFC 500.
In your case - Well, I'm not sure that Garmin will ever bother certifying the GFC 500 (or 600) for the Twinkie.
So an eventual GI 275 will at least allow you to keep the current autopilot going without a vacuum system.