Great question. In this case, all storage is going to be 10Gb, but several legacy hosts are going to be 1Gb. Uplink will also be 10Gb to core. Yes, in addition to iSCSI jumbos, some additional buffering capability to accommodate the rate changes could be needed.
Here's where I am at on this as of right now. I've been in touch with a Meraki field SE who pinged his broader team, my team within a large VAR, and solicited feedback on a popular internet forum. I'm getting zero encouragement to go with the MS425 in this application. It's a shame because my customer is a perfect target for Meraki in terms of the impact cloud management will have on their efficiency, but I'll have to go with WLAN only for now. Since they are "IT-lite" they are not a good case for a science experiment. Hopefully I can move their access layer switching to Meraki next year, but it's not in the budget this year.
If anyone pops up this evening that wants to make a case fo the MS425 in a iSCSI ToR application, I'm still all ears, but tomorrow it goes to the customer.