That large of a drive could definitely be a problem, along with OS 9.1. That's virtually the same size partition and same OS that's on the G4 tower I have had problems with connecting to from Macs of the Plus's vintage.
I didn't mean to use a boot disk to connect to the Performa. I meant that you could install a full System 7.0 onto the Plus from the set of installation disks you make. If the Plus had a 1.4 MB floppy drive, you could use Apple's System 7.5 Network Access Disk to access the Performa, but there's no way that's going to work on an 800K disk.
I think once you install a full System 7.0 installation, you may have better luck connecting to an AppleShare server so you can update to 7.0.1. Certainly the interface for configuring networking will be more familiar to you than that found in System 6. Even if we still have no luck, there's little wrong with System 7.0, as long as you install the System 7 Tune-Up, which may be available on Apple's website, or I can send you a copy. It will fit on an 800K disk so that you can install it.
Running any version of 7.5 on the Plus is silly, in my opinion. Not only is it going to strap you for RAM, but there's very little real advantage. Most things you can do on a Plus in 7.5, you can do in 7.0 -- I run my Plus under 7.0.1 as a web server. Unless you have a specific application where you need the features of 7.5, I'd say definitely stick with 7.0. Not to mention 7.0 still maintains a lot of that "classic nostalgia," which is probably more than half the reason you want to get the Plus up and running in the first place!
And one more thing . . .
Your Plus has an external, SCSI hard disk. You can plug this drive into your Performa and either install System 7.0/7.0.1 onto the drive by running the installer on the Performa, or just drop the installer files onto the drive and run the install once you get back on the Plus.
I didn't mean to use a boot disk to connect to the Performa. I meant that you could install a full System 7.0 onto the Plus from the set of installation disks you make. If the Plus had a 1.4 MB floppy drive, you could use Apple's System 7.5 Network Access Disk to access the Performa, but there's no way that's going to work on an 800K disk.
I think once you install a full System 7.0 installation, you may have better luck connecting to an AppleShare server so you can update to 7.0.1. Certainly the interface for configuring networking will be more familiar to you than that found in System 6. Even if we still have no luck, there's little wrong with System 7.0, as long as you install the System 7 Tune-Up, which may be available on Apple's website, or I can send you a copy. It will fit on an 800K disk so that you can install it.
Running any version of 7.5 on the Plus is silly, in my opinion. Not only is it going to strap you for RAM, but there's very little real advantage. Most things you can do on a Plus in 7.5, you can do in 7.0 -- I run my Plus under 7.0.1 as a web server. Unless you have a specific application where you need the features of 7.5, I'd say definitely stick with 7.0. Not to mention 7.0 still maintains a lot of that "classic nostalgia," which is probably more than half the reason you want to get the Plus up and running in the first place!
And one more thing . . .
Your Plus has an external, SCSI hard disk. You can plug this drive into your Performa and either install System 7.0/7.0.1 onto the drive by running the installer on the Performa, or just drop the installer files onto the drive and run the install once you get back on the Plus.